builtin/: add UNLEAKs

Add some UNLEAKs where we are about to return from `cmd_*`. UNLEAK the
variables in the same order as we've declared them. While addressing
`msg` in builtin/tag.c, convert the existing `strbuf_release()` calls as
well.

Signed-off-by: Martin Ågren <martin.agren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/checkout.c

@@ -1291,6 +1291,7 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
 		strbuf_release(&buf);
 	}
 
+	UNLEAK(opts);
 	if (opts.patch_mode || opts.pathspec.nr)
 		return checkout_paths(&opts, new.name);
 	else