read_loose_refs(): read refs using resolve_ref_recursively()

There is no need to call read_ref_full() or resolve_gitlink_ref() from
read_loose_refs(), because we already have a ref_store object in hand.
So we can call resolve_ref_recursively() ourselves. Happily, this
unifies the code for the submodule vs. non-submodule cases.

This requires resolve_ref_recursively() to be exposed to the refs
subsystem, though not to non-refs code.

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Reviewed-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

refs/refs-internal.h

@@ -650,4 +650,9 @@ void base_ref_store_init(struct ref_store *refs,
  */
 struct ref_store *get_ref_store(const char *submodule);
 
+const char *resolve_ref_recursively(struct ref_store *refs,
+				    const char *refname,
+				    int resolve_flags,
+				    unsigned char *sha1, int *flags);
+
 #endif /* REFS_REFS_INTERNAL_H */