more mailscanner ideas

[Matthew Byng-Maddick]

[copied to Tony, because I mentioned it to him in the pub]

This one is a way of maintaining a separate CustomConfig-style file where
Mailscanner admins can keep their own code.

It uses UNIVERSAL::can, which works on at least perl 5.005_03, but almost
certainly before that too. This means that it can fail nicely if no Init
or End function is specified.

The patch is available at:
  http://colon.colondot.net/~mbm/ald-stuff/mailscanner.customconfig.patch
and is against MailScanner-4.28.6

Anyway, see what you think.

Matthew