Repair Git#ls_files for bare repos.

Noticed that [the gollum-lib tests](https://github.com/gollum/gollum-lib/blob/master/test/test_wiki.rb#L370) were expecting only 1 hit for a search that should have returned 2 (filename and content of blob both match). Will implement this fix first, then release a new version of the adapter gem, then fix gollum-lib's tets.