convert_git: avoid returning two entries for the same file in getchanges
This could happen in merge changesets if the merged file was different
from both parents.
% unbundle
4 files updated, 0 files merged, 0 files removed, 0 files unresolved
a
d/b
% move and copy
a
d/b
% bundle
pulling from ../symlinks.hg
requesting all changes
adding changesets
adding manifests
adding file changes
added 2 changesets with 6 changes to 6 files
(run 'hg update' to get a working copy)
5 files updated, 0 files merged, 0 files removed, 0 files unresolved
a
a
d/b