make copy_ref globally available

This is a useful function, and we have already made the
similar alloc_ref and copy_ref_list available.
Signed-off-by: NJeff King <peff@peff.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

remote.c

@@ -896,7 +896,7 @@ struct ref *alloc_ref(const char *name)
 	return alloc_ref_with_prefix("", 0, name);
 }
 
-static struct ref *copy_ref(const struct ref *ref)
+struct ref *copy_ref(const struct ref *ref)
 {
 	struct ref *cpy;
 	size_t len;

remote.h

@@ -70,7 +70,7 @@ struct refspec {
 extern const struct refspec *tag_refspec;
 
 struct ref *alloc_ref(const char *name);
-
+struct ref *copy_ref(const struct ref *ref);
 struct ref *copy_ref_list(const struct ref *ref);
 
 int check_ref_type(const struct ref *ref, int flags);