[Dovecot] Cannot authenticate with new Red Hat/Fedora SHA512

[John Cooper]

RHEL6 and Fedora 14 use an improved password algorithm of SHA512 on a 
brand new install of the OS (:$6$ in shadow file).

cat /etc/shadow
user1:$6$<salt>$<password>:15006:0:99999:7:::

I cannot get dovecot to authenticate. I've search for a way to change 
the default algorithm in dovecot and found you should use CRYPT but I 
don't know what to put in the /etc/dovecot/dovecot.conf or 
/etc/dovecot/conf.d/*

Can this be done or do you need to use an alternate password file with MD5?

Thanks, John.