Fix notifications when adding package link dir

When adding a new package link directory, the volume would only be
notified about the addition of the directory itself, not of the addition
of its contents. Add a new PackageLinkDirectory::NotifyDirectoryAdded()
which does the whole job and use it in
PackageLinksDirectory::AddPackage().

Implement more virtuals in Node and Directory

* Node: Add default implementations for UserID(), GroupID(),
OpenAttributeDirectory(), and OpenAttribute().
* Directory: Add default implementations for Mode() and FileSize().
* Remove the respective hook implementations in the PackageLink*
classes.

Add dependency package links

The links appear, but the dependency resolution doesn't seem to work
correctly yet.

Move PackageLinkDirectory::Link to own file

And rename it to PackageLinkSymlink.

Resolve dependencies to resolvables

Fix package link updates/node monitoring

* PackageLinksListener: Rename methods from *Directory*() to *Node*()
and change parameter to Node*. Also add a *Changed() method.
* PackageLinkDirectory: Update only when necessary and what is necessary
(currently only the self link).

Add Node::Init() flags parameter

* Add Node::Init() flags:
- NODE_FLAG_KEEP_NAME: Take over ownership of the name.
- NODE_FLAG_CONST_NAME: Don't copy the name -- it's a constant that
lives at least as long as the object.
* Remove Init() implementations in derived classes that just call the
base class version.

Create self package link

Add package link directories to system volume

* Add PackageLinksListener interface. It is used by
PackageLink[s]Directory to notify a listener about changes.
* Volume does now implement PackageLinksListener and recursively adds/
removes package link directories.

This makes the package link directories appear at least. They are still
empty.

WIP: Create empty package links directories

* Rename PackageFamily to PackageLinkDirectory and derive from
Directory.
* PackageLinksDirectory: Add the PackageLinkDirectory objects as
children and remove the no longer needed hash table (we use the
Directory's child hash table).

Fix notifications when adding package link dir

When adding a new package link directory, the volume would only be
notified about the addition of the directory itself, not of the addition
of its contents. Add a new PackageLinkDirectory::NotifyDirectoryAdded()
which does the whole job and use it in
PackageLinksDirectory::AddPackage().

Implement more virtuals in Node and Directory

* Node: Add default implementations for UserID(), GroupID(),
OpenAttributeDirectory(), and OpenAttribute().
* Directory: Add default implementations for Mode() and FileSize().
* Remove the respective hook implementations in the PackageLink*
classes.

Add dependency package links

The links appear, but the dependency resolution doesn't seem to work
correctly yet.

Move PackageLinkDirectory::Link to own file

And rename it to PackageLinkSymlink.

Resolve dependencies to resolvables

Fix package link updates/node monitoring

* PackageLinksListener: Rename methods from *Directory*() to *Node*()
and change parameter to Node*. Also add a *Changed() method.
* PackageLinkDirectory: Update only when necessary and what is necessary
(currently only the self link).

Add Node::Init() flags parameter

* Add Node::Init() flags:
- NODE_FLAG_KEEP_NAME: Take over ownership of the name.
- NODE_FLAG_CONST_NAME: Don't copy the name -- it's a constant that
lives at least as long as the object.
* Remove Init() implementations in derived classes that just call the
base class version.

Create self package link

Add package link directories to system volume

* Add PackageLinksListener interface. It is used by
PackageLink[s]Directory to notify a listener about changes.
* Volume does now implement PackageLinksListener and recursively adds/
removes package link directories.

This makes the package link directories appear at least. They are still
empty.

WIP: Create empty package links directories

* Rename PackageFamily to PackageLinkDirectory and derive from
Directory.
* PackageLinksDirectory: Add the PackageLinkDirectory objects as
children and remove the no longer needed hash table (we use the
Directory's child hash table).