mail/dovecot, mail/dovecot-pigeonhole: upgrade to 2.3.7.1 and 0.5.7.1 respectively.

These releases fix the reported regressions in v2.3.7 & v0.5.7.

Dovecot core:

• Fix TCP_NODELAY errors being logged on non-Linux OSes
• lmtp proxy: Fix assert-crash when client uses BODY=8BITMIME
• Remove wrongly added checks in namespace prefix checking

Pigeonhole:

• dsync: Sieve script syncing failed if mailbox attributes weren't enabled.