The sieve_result_execute() function returned the wrong status result.

Implmented reporting full Pigeonhole version with hg tag so that builds between releases can be distinguished.
Copied from Dovecot for the most part.

This was caused by a circular reference.

Storage flag checks were bogus.

lib-sieve: Restructured result execution, so that all actions which involve mail storage are always committed before all others.

lib-sieve: Implemented sieve_redirect_envelope_from setting, which allows configuring the envelope sender of redirected messages.
Can either be set to the envelope sender, recipient, or orignal recipient of the processed message or it can be set explicitly to a static address.

It should only subscribe it when it is newly created.

These caused a BUG error to be reported during delivery.
Solved by signalling the occurrence of storage errors as a separate execution status flag, rather than querying the last storage itself for errors, which won't work.

Mail storage errors now trigger a runtime error.

No longer needed to create the temp directory.