Released Pigeonhole v0.4.7.rc1 for Dovecot v2.2.16.rc1

[E.B.]

> Last time I had a few stupid problems in the releases, so
> I'll follow
> Timo's example and I release an RC first.
> 
> The highlights include the implementation of the index and
> metadata
> extensions. Quite a few bugs are fixed as well.

When I compiled and installed this, Sieve scripts were being ignored. Not
sure if it's my own stupid mistake, but when I put v0.4.6 back in place, it
worked fine. No configuration changes, only make install on the different
sources and restart dovecot.