bpy/rna api class feature

- python defined classes will be used when available (otherwise automaically generated metaclasses are made as before)
- use properties rather then functions for python defined rna class's
- call the classes getattr AFTER doing an RNA lookup, avoids setting and clearing exceptions for most attribute lookups, tested UI scripts are ~25% faster.
- extending rna py classes this way is a nicer alternative to modifying the generated metaclasses in place.

Example class

--- snip
class Object(bpy.types.ID):

    def _get_children(self):
        return [child for child in bpy.data.objects if child.parent == self]

    children = property(_get_children)
--- snip

The C initialization function looks in bpy_types.py for classes matching RNA structure names, using them when available.
This means all objects in python will be instances of these classes.
Python properties/funcs defined in ID py class will also be available for subclasses for eg. (Group Mesh etc)

source/blender/python/intern/bpy_rna.h

@@ -64,6 +64,7 @@ typedef struct {
 /* cheap trick */
 #define BPy_BaseTypeRNA BPy_PropertyRNA
 
+void      BPY_rna_init( void );
 PyObject *BPY_rna_module( void );
 void	  BPY_update_rna_module( void );
 /*PyObject *BPY_rna_doc( void );*/