Blender Git Loki

Extra generic errors for Scene, Groups and Metaballs to raise errors when trying to do anything with a python objects thats had its data removed in Blender.

Added to existing scn.objects
scn.objects.active (get/set the active object for the scene)

scn.objects.selected - an iterator that only uses selected objects
scn.objects.context - an iterator on objects in the user context (visible in the current 3d views layer and selected)
These are the same type as scn.objects but .add() .remove() .new() .active etc raise errors. so scn.objects.selected.add() will raise an error.

Made nested loops possible with scn.objects, metaball.elements and ob.modifiers, by initializing the iter value as NULL and creating copys of the pyobject when _getIter() is called if ->iter is not NULL.
This is how pythons xrange() works.