get_fetch_map(): tighten checks on dest refs

The code to check the refname we store the fetched result locally did not
bother checking the first 5 bytes of it, presumably assuming that it
always begin with "refs/".  For a fetch refspec (or the result of applying
wildcard on one), we always want the RHS to map to something inside
"refs/" hierarchy, so let's spell that rule out in a more explicit way.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

remote.c

@@ -1402,8 +1402,8 @@ int get_fetch_map(const struct ref *remote_refs,
 
 	for (rmp = &ref_map; *rmp; ) {
 		if ((*rmp)->peer_ref) {
-			if (check_refname_format((*rmp)->peer_ref->name + 5,
-				REFNAME_ALLOW_ONELEVEL)) {
+			if (prefixcmp((*rmp)->peer_ref->name, "refs/") ||
+			    check_refname_format((*rmp)->peer_ref->name, 0)) {
 				struct ref *ignore = *rmp;
 				error("* Ignoring funny ref '%s' locally",
 				      (*rmp)->peer_ref->name);