Blender Git Loki

Alembic: fixed importer

The importer was guessing whether an Alembic IXform object was part of a
child object, or should be represented as an Empty in Blender. By reversing
the order in which objects are visited, the children can now claim their
parent as part of the same object (so IPolyMesh claims its parent IXform
as part of the same Blender object). This results in much less guesswork.

I've also removed similar guesswork from the code that sets parent pointers,
by simply searching for the parent in a hierarchical way, instead of trying
to predict (again) which IXforms were turned into empties.

Also, visit_object() now actually visits the object -- previously it only
visited its children, and assumed the object it was called on was already
handled by a previous call.