t / t4013 / diff.diff_--no-index_--raw_--abbrev=4_dir2_diron commit help_unknown_ref(): check for refname ambiguity (2ed2e19)
   1$ git diff --no-index --raw --abbrev=4 dir2 dir
   2:000000 100644 0000... 0000... A        dir/sub
   3$