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/shhg init aecho a > a/ahg --cwd a ci -A -m ahg clone a becho b > b/bhg --cwd b ci -A -m bchmod 100 a/.hg/storehg --cwd b push ../achmod 700 a/.hg/store