Merge branch 'fc/completion'

* fc/completion: completion: remove __git_index_file_list_filter() completion: add space after completed filename completion: add hack to enable file mode in bash < 4 completion: refactor __git_complete_index_file() completion: refactor diff_index wrappers completion: use __gitcompadd for __gitcomp_file completion; remove unuseful comments completion: document tilde expansion failure in tests completion: add file completion tests