Blender Git Loki

LibOverride: refactor recursive resync.

We need to re-evaluate what needs to be resynced after each step of
processing overrides from a given 'indirect level' of libraries.
Otherwise, recusrive overrides (overrides of linked overrides) won't
work.

Note that this should not change too much in practice currently, since
there are other issues with recursive overrides yet.

Also, checks (CLOG errors) added show that some ID (node trees) seem to
be detected as needing resynced even after beig just resynced, this
needs further investigation still. Could be though that it is due to
limit currently set on nodetrees, those are always complicated
snowflakes to deal with...