Don't generate git patches that rename a file to multiple destinations
With this patch, instead of generating N renames, we'll generate
1 rename and N-1 copies.
Ideally the rename should come after the copies instead of before
them, but that'd be harder to do.
# should print nothing
# should print ? b/x
? b/x
# should print A b/x
A b/x
# should forget b/x
forgetting b/x
# should print nothing