[Dovecot] Catch22: user needs space to fix out of space condition

[Joseph Tam]

Thanks to all who've made suggestions.  It seems removing dotlocks as
a locking method is the way to go.  There is another dotlock locking
variant mentioned in 10-mail.conf that seems to address this situation
for those that can't get away from dotlocks:

 	#  dotlock_try: Same as dotlock, but if it fails because of permissions or
 	#               because there isn't enough disk space, just skip it.
 	mbox_write_locks = dotlock_try fcntl

Joseph Tam <jtam.home at gmail.com>