[Dovecot] API changes and plugins

There's been quite a lot of changes in CVS lately, mostly related to API changes but also some index file changes. They've both had very little testing, so there's probably a few bugs left. Especially mbox users should be careful. pop3 might also be deleting wrong messages..

Anyway. The new mail storage API should allow plugins to hook into pretty much any operation they want to. It's not exactly pretty with C syntax, but I think conceptually it's nice object oriented design :)

There's example (non-working) quota plugin at:

http://dovecot.procontrol.fi/patches/quota.c

I also built 0.99.11-test3 from current CVS:

http://dovecot.procontrol.fi/test/