for-each-ref: implement missing tag values

The "type" and "object" fields for tags were accepted as
valid atoms, but never implemented. Consequently, they
simply returned the empty string, even for valid tags.

Noticed by Lea Wiemann.

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

builtin-for-each-ref.c

@@ -234,6 +234,13 @@ static void grab_tag_values(struct atom_value *val, int deref, struct object *ob
 			name++;
 		if (!strcmp(name, "tag"))
 			v->s = tag->tag;
+		else if (!strcmp(name, "type") && tag->tagged)
+			v->s = typename(tag->tagged->type);
+		else if (!strcmp(name, "object") && tag->tagged) {
+			char *s = xmalloc(41);
+			strcpy(s, sha1_to_hex(tag->tagged->sha1));
+			v->s = s;
+		}
 	}
 }