mailpipe: add a warning message before loading a message from a stream.

This reminds you if you forget to use the `--mailbox` option when
calling `pg.py`, and the process hangs waiting for a message on stdin.

diff --git a/pygrader/mailpipe.py b/pygrader/mailpipe.py
index b2542735286ff7add8bfd294be04194cb7edff46..dd88d824cad37315ee9a062219e3eb6d664c063c 100644 (file)
--- a/pygrader/mailpipe.py
+++ b/pygrader/mailpipe.py
@@ -610,6 +610,7 @@ def _load_messages(course, stream, mailbox=None, input_=None, output=None,
                    continue_after_invalid_message=False, respond=None,
                    dry_run=False):
     if mailbox is None:
+        _LOG.debug('loading message from {}'.format(stream))
         mbox = None
         messages = [(None,_message_from_file(stream))]
         if output is not None: