cron - stop console logging

[Matt Miller <debianuser@fastmail.fm>]

cron is logging to the active console and I don't know how to turn it 
off.  Every couple minutes I get something like:

cron(pam_unix)[15457]: session opened for user mail (uid=0)
cron(pam_unix)[15457]: session closed for user mail

The cron man pages says that cron logs to the syslog facility 'cron,' 
and /etc/syslog.conf says:

cron.*		/var/log/cron.log

so I would expect that these messages I'm getting on the console would 
go to that file, and not to the console.  However the specified file 
does not even exist.