[Spambayes] mboxtrain.py chokes on non-existent directories

[Skip Montanaro]

    Charl> I you run mboxtrain.py with -g or -s set to a non-existent
    Charl> directory you end up with and error like:

    ...

I just checked in a change to mboxtrain.py but can't really test it because
I don't use that code.  Please "cvs up" and give it a try.

Skip