completion: handle other variants of "branch -m"

We didn't special-case "branch -M" (with a capital M) the same as
"branch -m", nor any of the "--copy" variants. As a result these offered
any ref as the next candidate, and not just branch names.

Note that I rewrapped case-arm line since it's now quite long, and
likewise the one below it for consistency. I also re-ordered the
existing "-D" to make it more obvious how the cases group together.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/completion/git-completion.bash

@@ -1438,8 +1438,10 @@ _git_branch ()
 	while [ $c -lt $cword ]; do
 		i="${words[c]}"
 		case "$i" in
-		-d|--delete|-D|-m|--move)	only_local_ref="y" ;;
-		-r|--remotes)		has_r="y" ;;
+		-d|-D|--delete|-m|-M|--move|-c|-C|--copy)
+			only_local_ref="y" ;;
+		-r|--remotes)
+			has_r="y" ;;
 		esac
 		((c++))
 	done