Can we have a message when agent expiry is finished?

[Mike McEwan <mike@lotusland.demon.co.uk>]

  Just a teensy little request - can a message be whacked on the end of 
a `gnus-agent-expire' run. 

  Can expiry not be conducted on *all* articles older than a certain
date, regardless of whether they have been marked read or not (with
the exception of ticked)?

  I realise I can do a `c' on a summary buffer limited by date, and
then run expiry. But a variable or function bringing about this
behaviour would be so much easier.

  Useful feature? Should I just knock something up for myself and
leave everyone else alone?

-- 
Mike.