object: rename function 'typename' to 'type_name'

Rename C++ keyword in order to bring the codebase closer to being able
to be compiled with a C++ compiler.

Signed-off-by: Brandon Williams <bmwill@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

reachable.c

@@ -94,7 +94,7 @@ static void add_recent_object(const struct object_id *oid,
 		break;
 	default:
 		die("unknown object type for %s: %s",
-		    oid_to_hex(oid), typename(type));
+		    oid_to_hex(oid), type_name(type));
 	}
 
 	if (!obj)