Remove superfluous checks

More abstraction in GenericIndexIterator

* Move tree node operations to a subpolicy TreePolicy.
* Add a GenericIndexIteratorTreePolicy templatized over the policy,
implementing the tree policy for the standard indices.

Remove TwoKeyAVLTree from kernel utils again

It's not ready for shared use yet.

GenericIndexIterator: Fix NameIndex dependency

Next() was still copying the name. Add a GetNodeValue() method to the
policy that fetches the value instead.

Refactor NameIndexIterator into template class

Create template class GenericIndexIterator from NameIndexIterator.

NodeListener::NodeChanged(): Provide old value

* Add interface OldNodeAttributes an instance of which is passed to
NodeListener::NodeChanged() to provide the old attribute values
(currently only modification time and file size).
* Also extend PackageLinksListener::PackageLinkNodeChanged() with a
OldNodeAttributes parameter.
* Add OldNodeAttributes implementations for PackageLinkSymlink (inner
class OldAttributes) and UnpackingNode (OldUnpackageNodeAttributes).

~NameIndex(): Make more robust

Remove the listener only, if it was registered.

Name::Index(): Fix initialization order

Add the node listener directly after calling the base class Init().
Otherwise, on error, the we could try to remove the listener although it
wasn't added in the first place.

Simplify [Abstract]IndexIterator interface

* Remove Current() and Previous() and add a HasNext() instead.
* Reimplement NameIndexIterator. It directly works with tree nodes
instead of using an iterator, now.

Fix NameIndexPrimaryKeyCompare

It was actually returning whether the names where not equal.

Cleanup

Add NameIndex class and create instance in Volume

Remove superfluous checks

More abstraction in GenericIndexIterator

* Move tree node operations to a subpolicy TreePolicy.
* Add a GenericIndexIteratorTreePolicy templatized over the policy,
implementing the tree policy for the standard indices.

Remove TwoKeyAVLTree from kernel utils again

It's not ready for shared use yet.

GenericIndexIterator: Fix NameIndex dependency

Next() was still copying the name. Add a GetNodeValue() method to the
policy that fetches the value instead.

Refactor NameIndexIterator into template class

Create template class GenericIndexIterator from NameIndexIterator.

NodeListener::NodeChanged(): Provide old value

* Add interface OldNodeAttributes an instance of which is passed to
NodeListener::NodeChanged() to provide the old attribute values
(currently only modification time and file size).
* Also extend PackageLinksListener::PackageLinkNodeChanged() with a
OldNodeAttributes parameter.
* Add OldNodeAttributes implementations for PackageLinkSymlink (inner
class OldAttributes) and UnpackingNode (OldUnpackageNodeAttributes).

~NameIndex(): Make more robust

Remove the listener only, if it was registered.

Name::Index(): Fix initialization order

Add the node listener directly after calling the base class Init().
Otherwise, on error, the we could try to remove the listener although it
wasn't added in the first place.

Simplify [Abstract]IndexIterator interface

* Remove Current() and Previous() and add a HasNext() instead.
* Reimplement NameIndexIterator. It directly works with tree nodes
instead of using an iterator, now.

Fix NameIndexPrimaryKeyCompare

It was actually returning whether the names where not equal.

Cleanup

Add NameIndex class and create instance in Volume