Blender Git Loki

Attempt to fix the NodeTree issue.

So, idea is, since mat/tex/scene/etc. nodetrees are owned by their respective IDs
(those nodetree do not exist in Main, they are systematically freed with their ower IDs, etc.),
we should not treat them as IDs in IDlooper, but rather as mere sub-data, and hence directly
loop over the IDs of those nodetrees.

From quick check it seems to work, but this needs to be confirmed as a valid idea!