salvaged: properly deal with salvaged file during copy tracing
When salvaged files are encountered, the removal have been reverted and we
should keep the rename information from the other side.
The conditional was starting to be quite hairy, so we spell it out in multiple
elif case for readability.
This fixes the associated test cases introduced a while back. The changeset centric copy tracing is now (known) bug free.
Differential Revision: https://phab.mercurial-scm.org/D9130