This check is pretty slow, and there aren't a whole lot of duplicate
objects created during the NoteDb migration. They will be cleaned up
during the next GC, which the admins can run at their leisure.
Update JGit with an additional commit to make this method public.
Change-Id: I0092f009554a6bc98f2ecc33040c6a0db97dc9dd
6979ccc3d5