Updated to Qt 4.8 with some back-ported fixes from Qt 4.8.1.

Removed carrier types from the ML; modules that support non-scalar voxel types can access these types directly now. See CarrierTypes removed.

Base objects can now be reference-counted by using a new base class RefCountBase. Wrapped objects can be used with reference-counting in Python scripting as well.

New Base class AbstractItemModel implements a hierarchical item list and offers a MDL control for viewing the data.

Example modules using the AbstractItemModel are FileSystemModelView and FileSystemModelData.

User data and preferences directories on Windows and Linux have been standardized.