allow user@hostname in commonapache log

Allow user@hostname in the field userid. So it is possible to parse:

127.0.0.1 user-identifier frank@domain.com [10/Oct/2000:13:55:36 -0700] "GET /apache_pb.gif HTTP/1.0" 200 2326

with COMMONAPACHELOG pattern.
email doesn't have to have a dot in it. Maybe we should just make the apache pattern do %{NOTSPACE:user} ?