completion: --list option for git-branch

Signed-off-by: Ralf Thielow <ralf.thielow@googlemail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/completion/git-completion.bash

@@ -1152,7 +1152,7 @@ _git_branch ()
 		__gitcomp "
 			--color --no-color --verbose --abbrev= --no-abbrev
 			--track --no-track --contains --merged --no-merged
-			--set-upstream --edit-description
+			--set-upstream --edit-description --list
 			"
 		;;
 	*)