completion: show can take both revlist and paths

The 'git show' completion uses __git_complete_file (aliased to __git_complete_revlist_file), because accepts <tree-ish>:<path> as well as <commit-ish>. But the command also accepts range of commits in A..B notation, so using __git_complete_revlist_file is more appropriate. There still remain two users of __git_complete_file, completions for "archive" and "ls-tree". As these commands do not take range notation, and "git show" no longer uses __git_complete_file, the implementation of it can be updated not to complete ranges, but that is a separate topic. Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>