Added support for JavaScript mail processors configured in mailproc.cfg
with "?scriptname". See ctrl/mailproc.cfg and exec/mailproc_example.js for
details.
Some cosemtic changes to log entries.
Bugfix: if a mail processor rejected a message, the server could segfault if
the sending server reset the session or attempted another message. Also,
temp files (recipient list and msg text) would be orphaned in the data_dir.