More WriteAttr -> WriteAttrString cleanup across the tree.

Some of these were correct as they were ... but most weren't.
There are a variety of other correct ones I didn't change over yet
that someone else probably should (GCI task?).

POP3: Actually return B_TIMED_OUT not just B_ERROR on timeouts.

POP3: Remove direct usage of OpenSSL.

It already uses BSecureSocket without checking for USE_SSL,
so just assume we have SSL no matter what.

BMailProtocol: Removed delete/append methods.

* The mail system is file based which makes these methods pretty much
superfluous.

IMAP: setting flags, and body fetching works now.

* The direct methods in BMailProtocol now forward the request to the
looper; it's no longer the mail_daemon's responsibility to know
anything about that protocol.
* It's in desperate need of refactoring, but it doesn't hurt to add
it to the repository as is.

SMTP works again.

* The message to send the mails never made it to the add-on looper.
* Mail protocol threads now have names.
* Added a "public" BOutboundMailProtocol::SendMessages() call that sends
itself a message (even the correct one this time).

POP3 mail add-on: set unread attribute on fetched mail

- ...to make the new mails show up in the "New E-Mail" query

POP3 mail add-on: fix fetching mail bodies without limit

* "No limit set" is signaled by a negative value in fFetchBodyLimit
(cf. logic in POP3Protocol::SyncMessages())

IMAP,POP3,NewMailNotification: fixed x86_64 build.

* Notifier::HeaderFetched(): fixed the method signature (go figure how it could
build on x86).
* POP3: fSizes type is now std::vector<size_t> instead of BList. Please review.
off_t might be a better choice.
* added the mail_daemon add-ons to the Haiku package again.

IMAP: downloading mails is now working.

* Changed the way the attributes are written to make sure that everything
that can be written once is in fact written just once.
* The rename code in BMailProtocol::_ProcessFetchedHeader() was broken,
and caused the hang of the last commit.

Mail Kit: Changed how filter changes work.

* BMailFilter::HeaderFetched() now only alters the entry_ref, and returns
B_MOVE_MAIL_ACTION to move a mail.
* Instead of potentially moving the file around several times, the
BMailProtocol now takes care of carrying out the filter action just once,
including trying to make the file name unique.
* This also allows the IMAP add-on to know the final location of the mail,
and thus downloading a message actually works.
* However, with my test inbox, it currently hangs, and a current Debugger does
not work on my older system -- I guess I need to update.
* Replaced the duplicated space mechanism within the "HaikuMailFormatFilter"
that is substantially faster, and handles all whitespace, not just spaces.
It will also replace tabs with spaces.

pop3: minor cleanup.

pop3: Fixed maintaining fSizes list, and more.

* The list was filled, but never emptied.
* If SyncMessages() was called more than once for the same POP3 instance,
this could garble the mails retrieved in the second run.
* Maintain the total size of mails in fSizes to be able to report progress
in more detail.
* Also adapted progress reporting to the argument changes made in MailProtocol
earlier.
* Minor cleanup.

Work in progress of mail rework.

* Not everything compiles; all protocols, and inbound filters do, though.
* Renamed a few classes to give a better idea what they are for; prefixed
public classes with the 'B' prefix.
* Moved ProtocolConfigView's classes into the BPrivate namespace.
* Moved BMailFilter into its own file.
* Added BMailFilter::DescriptiveName(). This is now used by the RuleFilter
in order to give a description of what it's doing (ie. no more dozens of
"Rule filter" entries in the preferences).
* Removed no longer used MailAddon.h.
* Renamed Addon to AddOn where found, since that is more consistent with the
rest of the API.
* Merged the former MailProtocol with the former MailProtocolThread; the
differentiation between those two was pretty messy.
* All configuration views touched so far are now using the layout kit.
* The RuleFilter is currently broken functionality wise; I have not yet decided
how to solve the stuff it uses (TriggerFileMove() does not exist anymore,
for example).
* BMailAddOnSettings (formerly known as AddonSettings) now directly subclass
BMessage; there are no Settings() and EditSettings() method anymore. The
class uses a copy of itself to determine whether or not it has been changed.
* Lots of cleanup.

Renamed pop3.{cpp|h} to POP3.{cpp|h}.

POP3 mail add-on: set unread attribute on fetched mail

- ...to make the new mails show up in the "New E-Mail" query

POP3 mail add-on: fix fetching mail bodies without limit

* "No limit set" is signaled by a negative value in fFetchBodyLimit
(cf. logic in POP3Protocol::SyncMessages())

IMAP,POP3,NewMailNotification: fixed x86_64 build.

* Notifier::HeaderFetched(): fixed the method signature (go figure how it could
build on x86).
* POP3: fSizes type is now std::vector<size_t> instead of BList. Please review.
off_t might be a better choice.
* added the mail_daemon add-ons to the Haiku package again.

IMAP: downloading mails is now working.

* Changed the way the attributes are written to make sure that everything
that can be written once is in fact written just once.
* The rename code in BMailProtocol::_ProcessFetchedHeader() was broken,
and caused the hang of the last commit.

Mail Kit: Changed how filter changes work.

* BMailFilter::HeaderFetched() now only alters the entry_ref, and returns
B_MOVE_MAIL_ACTION to move a mail.
* Instead of potentially moving the file around several times, the
BMailProtocol now takes care of carrying out the filter action just once,
including trying to make the file name unique.
* This also allows the IMAP add-on to know the final location of the mail,
and thus downloading a message actually works.
* However, with my test inbox, it currently hangs, and a current Debugger does
not work on my older system -- I guess I need to update.
* Replaced the duplicated space mechanism within the "HaikuMailFormatFilter"
that is substantially faster, and handles all whitespace, not just spaces.
It will also replace tabs with spaces.

pop3: minor cleanup.

pop3: Fixed maintaining fSizes list, and more.

* The list was filled, but never emptied.
* If SyncMessages() was called more than once for the same POP3 instance,
this could garble the mails retrieved in the second run.
* Maintain the total size of mails in fSizes to be able to report progress
in more detail.
* Also adapted progress reporting to the argument changes made in MailProtocol
earlier.
* Minor cleanup.

Work in progress of mail rework.

* Not everything compiles; all protocols, and inbound filters do, though.
* Renamed a few classes to give a better idea what they are for; prefixed
public classes with the 'B' prefix.
* Moved ProtocolConfigView's classes into the BPrivate namespace.
* Moved BMailFilter into its own file.
* Added BMailFilter::DescriptiveName(). This is now used by the RuleFilter
in order to give a description of what it's doing (ie. no more dozens of
"Rule filter" entries in the preferences).
* Removed no longer used MailAddon.h.
* Renamed Addon to AddOn where found, since that is more consistent with the
rest of the API.
* Merged the former MailProtocol with the former MailProtocolThread; the
differentiation between those two was pretty messy.
* All configuration views touched so far are now using the layout kit.
* The RuleFilter is currently broken functionality wise; I have not yet decided
how to solve the stuff it uses (TriggerFileMove() does not exist anymore,
for example).
* BMailAddOnSettings (formerly known as AddonSettings) now directly subclass
BMessage; there are no Settings() and EditSettings() method anymore. The
class uses a copy of itself to determine whether or not it has been changed.
* Lots of cleanup.

Renamed pop3.{cpp|h} to POP3.{cpp|h}.