Merge branch 'es/check-mailmap'

A new command to allow scripts to query the mailmap information.

* es/check-mailmap:
  t4203: test check-mailmap command invocation
  builtin: add git-check-mailmap command

contrib/completion/git-completion.bash

@@ -648,6 +648,7 @@ __git_list_porcelain_commands ()
 		cat-file)         : plumbing;;
 		check-attr)       : plumbing;;
 		check-ignore)     : plumbing;;
+		check-mailmap)    : plumbing;;
 		check-ref-format) : plumbing;;
 		checkout-index)   : plumbing;;
 		commit-tree)      : plumbing;;