Merge branch 'rr/complete-difftool-fixup'

"git difftool" can take both revs to be compared and pathspecs.
"git show" takes revs, revs:path and pathspecs.

* rr/complete-difftool-fixup:
  completion: show can take both revlist and paths
  completion: difftool takes both revs and files

diff --cc contrib/completion/git-completion.bash
Simple merge