Updated mail/postfix to 2.5.7

- (low) The installation/upgrade procedure did not automatically
  create the data_directory.

- (medium) In the "new queue manager", the _destination_rate_delay
  code needed to postpone the job scheduler updates after delivery
  completion, otherwise the scheduler could loop on blocked jobs.

- (low) The queue manager used <transport>_concurrency_failed_cohort_limit
  instead of <transport>_destination_concurrency_failed_cohort_limit
  as documented.

- (low) The SMTP client disabled MIME parsing despite non-empty
  settings for smtp_header_checks, smtp_mime_header_checks,
  smtp_nested_header_checks, or smtp_body_checks.

- (medium) The postsuper command re-enabled the SIGHUP signal when
  it was set to "ignore". This could result in random "Postfix
  integrity check failed" errors at boot time (POSIX SIGHUP death),
  causing Postfix not to start automatically.


(martti)