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.
#!/bin/sh
mkdir t
cd t
hg init
echo a > a
hg ci -Ama -d '1000000000 0'
echo b > b
hg branch b
hg ci -Amb -d '1000000000 0'
hg co -C 0
echo fast-forward
hg merge b
hg ci -Ammerge -d '1000000000 0'
echo bogus fast-forward should fail
hg merge b
echo done