Blender Git Loki

RNA: add new property falg for pointers (and collection), 'NO_OWNERSHIP'.

This flag means that the pointer does not 'own' the data it references.
This is the case of nearly all ID RNA pointers (NodeTrees will probably
again be some nasty exception here :( ), but also several other cases.

That kind of information is mandatory for complex processing over whole
data-blocks done in RNA, like some static override tasks (advanced
comparison...).