git convert: some versions of git use fatal: instead of error: I saw this behavior with git 1.7.12 on my Mac.

test-convert-git: stabilize corruption of test git repo This error would show up only intermittently since the test depended on the order of the directories returned by os.walk. The damage repository test would delete the first object file it came across. However, the order of the directory listing is arbitrary (it seems to depend on the filesystem). This meant that sometimes a commit object was deleted, sometimes a blob object and sometimes a tree object. So, fix by hardcoding which object to delete. Delete a commit object, a blob object and a tree object in three separate tests.