There should be more error checking for various things, in particular
sanity checking of the form variables passed in.

Could check username/password submitted against horde's copy of them
to make sure they match and if not reject it earlier.  Instead we are
currently waiting until the ftp connection fails to see if the password
is wrong.  This isn't very precise as the ftp connection could have
failed for other reasons.

Maybe set up some preferences for this?  Default subject/message text?

Add method to view current settings.

Alias support should be a config option, as not all vacation programs
support it.  Add support for multiple aliases rather than just one...
