Merge branch 'jk/peel-ref'

Speeds up "git upload-pack" (what is invoked by "git fetch" on the
other side of the connection) by reducing the cost to advertise the
branches and tags that are available in the repository.

* jk/peel-ref:
  upload-pack: use peel_ref for ref advertisements
  peel_ref: check object type before loading
  peel_ref: do not return a null sha1
  peel_ref: use faster deref_tag_noverify

builtin/pack-objects.c

@@ -2033,7 +2033,6 @@ static int add_ref_tag(const char *path, const unsigned char *sha1, int flag, vo
 
 	if (!prefixcmp(path, "refs/tags/") && /* is a tag? */
 	    !peel_ref(path, peeled)        && /* peelable? */
-	    !is_null_sha1(peeled)          && /* annotated tag? */
 	    locate_object_entry(peeled))      /* object packed? */
 		add_object_entry(sha1, OBJ_TAG, NULL, 0);
 	return 0;