Blender Git Loki

Proper handling of IDs in do_versions_after_liblink.

Basic idea is to store fileversion in Library datablock, and split again
Main by libraries after lib linking, do_versions_after_liblink on
those separated Mains, and merge again.

This allows to still have correct versions for each data-block in that
second do_versions step.

Initial resurrection of `do_versions_after_linking()`.