[Dovecot] Can't take user info from an alternate file

[dave at 661.org]

I'm positive I did everything right to get Dovecot to take usernames and 
passwords from /etc/dovecot/users, but it still goes for /etc/passwd and 
/etc/shadow.  The format of /etc/dovecot/users is 
"alice:{PLAIN}plaintextpassword" Here's my "doveconf -n":

# 2.0.19: /etc/dovecot/dovecot.conf
# OS: Linux 3.2.0-51-virtual x86_64 Ubuntu 12.04.2 LTS
auth_debug = yes
auth_verbose = yes
auth_verbose_passwords = plain
hostname = papasmurf.foobar.com
listen = *
mbox_write_locks = fcntl
passdb {
   args = scheme=PLAIN-MD5 username_format=%n /etc/dovecot/users
   driver = passwd-file
}
plugin {
   sieve = ~/.dovecot.sieve
   sieve_dir = ~/sieve
}
service auth {
   unix_listener /var/spool/postfix/private/auth {
     group = postfix
     mode = 0664
     user = postfix
   }
}
ssl_cert = </etc/ssl/certs/dovecot.pem
ssl_key = </etc/ssl/private/dovecot.pem
userdb {
   args = username_format=%n /etc/dovecot/users
   driver = passwd-file
}

I'm using Ubuntu Precise and version 2.0.19 of Dovecot.

-- 
David Griffith
dave at 661.org