Blender Git Loki

Readfile: Resurrect 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.

Note that this is not used currently in master (might be soon, though),
but is needed for 2.8 work.