mail/dovecot2-pigeonhole: upgrade to 0.4.19
ChangeLog:

• This release adjusts Pigeonhole to several changes in the Dovecot API, making it depend on Dovecot v2.2.31. Previous versions of Pigeonhole will produce compile warnings with the recent Dovecot releases (but still work ok).
• Fixed bug in handling of implicit keep in some cases. Implicit side-effects, such as assigned flags, were not always applied correctly. This is in essence a very old bug, but it was exposed by recent changes.
• include extension: Fixed segfault that (sometimes) occurred when the global script location was left unconfigured.