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>

submodule.c

@@ -831,7 +831,7 @@ static int check_has_commit(const struct object_id *oid, void *data)
 		return 0;
 	default:
 		die(_("submodule entry '%s' (%s) is a %s, not a commit"),
-		    cb->path, oid_to_hex(oid), typename(type));
+		    cb->path, oid_to_hex(oid), type_name(type));
 	}
 }