make "find_ref_by_name" a public function

This was a static in remote.c, but is generally useful.

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

cache.h

@@ -514,6 +514,8 @@ struct ref {
 #define REF_HEADS	(1u << 1)
 #define REF_TAGS	(1u << 2)
 
+extern struct ref *find_ref_by_name(struct ref *list, const char *name);
+
 #define CONNECT_VERBOSE       (1u << 0)
 extern struct child_process *git_connect(int fd[2], const char *url, const char *prog, int flags);
 extern int finish_connect(struct child_process *conn);