Log Message:
mail/dovecot2-pigeonhole: update to 0.5.7

Update dovecot2-pigeonhole to 0.5.7.

Changes
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+ vacation: Made the subject for the automatic response message produced
  by the Sieve vacation action configurable. Both the default subject
  (if the script defines none) and the subject template (e.g. used to
  add a subject prefix) can be configured.
- dsync: dsync-replication does not synchronize Sieve scripts.
- imap_sieve_filter: Reduce FILTER=SIEVE verbosity over IMAP connection.
- testsuite: Pigeonhole testsuite segfaulted if it was compiled with
  GCC 9