IMAP: Retrieve on-disk folder state async.

* Messages that we don't have info for during synchronization are now
collected, and synchronized once the folder state is available,
instead of waiting for that particular entry to become available
(without proper means to wait).

IMAP: Extra local messages are now deleted.

* When a message on the server is deleted, it will now be deleted
locally, too.

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.

IMAP: fixed GCC4 build.

IMAP: work in progress of downloading the mail body.

* Most things are in place now, we just try to download the body to the
wrong file, as the final location is currently unknown.
* Added local only kPartialMessage flag for mails, but it's not being
used yet.

IMAP: IMAPFolder now stores the last UID.

* So mails are no longer downloaded every time.

imap: Fetching headers is now working.

* No state is stored yet, though, so that all messages will be downloaded
over and over again.

imap: WIP of getting fetching headers to work.

* Changed the FetchListener mechanism quite a bit.
* Doesn't seem to work correctly yet, although most pieces are in
place now.

imap: Work in progress of connection setup.

* SelectCommand now correctly encodes the mailbox name again.
* Hierarchy separators from the LIST/LSUB commands are now properly parsed,
and taken into account.
* Folders in the file system are now created for mailboxes on the server,
supporting hierarchical mailbox names.
* A connection worker now has an IMAPFolder that handles the local side of the
mailbox, and an IMAPMailbox that handles the server side.
* Connection workers are now created/deleted, and setup correctly. They will
now also wait in case they don't have a mailbox until they get some.

IMAP: FolderList is supposed to be an interface.

* Made its methods pure virtual.

IMAP now compiles again with GCC 4.

Initial work on a class that manages an IMAP folder on disk.

IMAP: fixed GCC4 build.

IMAP: work in progress of downloading the mail body.

* Most things are in place now, we just try to download the body to the
wrong file, as the final location is currently unknown.
* Added local only kPartialMessage flag for mails, but it's not being
used yet.

IMAP: IMAPFolder now stores the last UID.

* So mails are no longer downloaded every time.

imap: Fetching headers is now working.

* No state is stored yet, though, so that all messages will be downloaded
over and over again.

imap: WIP of getting fetching headers to work.

* Changed the FetchListener mechanism quite a bit.
* Doesn't seem to work correctly yet, although most pieces are in
place now.

imap: Work in progress of connection setup.

* SelectCommand now correctly encodes the mailbox name again.
* Hierarchy separators from the LIST/LSUB commands are now properly parsed,
and taken into account.
* Folders in the file system are now created for mailboxes on the server,
supporting hierarchical mailbox names.
* A connection worker now has an IMAPFolder that handles the local side of the
mailbox, and an IMAPMailbox that handles the server side.
* Connection workers are now created/deleted, and setup correctly. They will
now also wait in case they don't have a mailbox until they get some.

IMAP: FolderList is supposed to be an interface.

* Made its methods pure virtual.

IMAP now compiles again with GCC 4.

Initial work on a class that manages an IMAP folder on disk.