Log Message:
Update to dovecot-1.0rc21.

Changes in dovecot-1.0rc20:

	+ dovecot: Added --log-error command line option to log an error, so
	  the error log is easily found.
	+ Added mail_log_max_lines_per_sec setting. Change it to avoid log
	  throttling with mail_log plugin.
	- Changing message flags was more or less broken in rc19
	- ACL plugin still didn't work without separate control directory
	- Some mbox handling fixes, including fixing an infinite loop
	- Some index file handling fixes
	- maildir quota: Fixed a file descriptor leak
	- If auth_cache was enabled and userdb returned "user unknown"
	  (typically only deliver can do that), dovecot-auth crashed.
	- mail_log plugin didn't work with pop3

Changes in dovecot-1.0rc21:

	- Cache file handling could have crashed rc20