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.
adding he
llo
abort: '\n' and '\r' disallowed in filenames
adding he
llo
abort: '\n' and '\r' disallowed in filenames
adding hell
o
abort: '\n' and '\r' disallowed in filenames
adding hell
o
abort: '\n' and '\r' disallowed in filenames
f he
llo he
llo
f hell
o hell
o