Support for this was added in Python 2.6 and 3.0.  We can't have
Python 3 compatibility without removing the old "except x, y" syntax,
and I think 3.x support is more imporant than 2.5 support.  In any
case, the existing irkerd has been using the new syntax since 3cc87513
(Truncate messages that are longer than 512 bytes and catch any
exceptions irclib throws about rejected messages, 2013-01-21), so this
commit is not a *new* break with 2.5 support.