Make push more verbose about illegal combination of options

It may be unclear that --all, --mirror, --tags and/or explicit refspecs
are illegal combinations for git push.

Git was silently failing in these cases, while we can complaint more
properly about it.

Signed-off-by: Marek Zawirski <marek.zawirski@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-push.c

@@ -59,8 +59,17 @@ static int do_push(const char *repo, int flags)
 	if (remote->mirror)
 		flags |= (TRANSPORT_PUSH_MIRROR|TRANSPORT_PUSH_FORCE);
 
-	if ((flags & (TRANSPORT_PUSH_ALL|TRANSPORT_PUSH_MIRROR)) && refspec)
-		return -1;
+	if ((flags & TRANSPORT_PUSH_ALL) && refspec) {
+		if (!strcmp(*refspec, "refs/tags/*"))
+			return error("--all and --tags are incompatible");
+		return error("--all can't be combined with refspecs");
+	}
+
+	if ((flags & TRANSPORT_PUSH_MIRROR) && refspec) {
+		if (!strcmp(*refspec, "refs/tags/*"))
+			return error("--mirror and --tags are incompatible");
+		return error("--mirror can't be combined with refspecs");
+	}
 
 	if ((flags & (TRANSPORT_PUSH_ALL|TRANSPORT_PUSH_MIRROR)) ==
 				(TRANSPORT_PUSH_ALL|TRANSPORT_PUSH_MIRROR)) {