Fix imap4d testsuite

The tests failed if MU_DEFAULT_SCHEME were set to anything, but mbox.

* imap4d/tests/atlocal.in (make_config): set .mailbox.mailbox-type=mbox.
* imap4d/list.c (imap4d_list): Use %s as the format.

@@ -317,6 +317,6 @@ imap4d_list (struct imap4d_session *session,
   free (cwd);
   free (ref);
   
-  return io_completion_response (command, status, resp_text[status]);
+  return io_completion_response (command, status, "%s", resp_text[status]);
 }
 

@@ -44,6 +44,7 @@ namespace other {
 mailbox {
 	folder "$CWD";
 	mailbox-pattern "$CWD/INBOX";
+	mailbox-type mbox;
 }	
 EOT
 }