[Dovecot] Dovecot v2.0 hg tree

http://hg.dovecot.org/dovecot-2.0/

I just did the initial commit for master process rewrite, which marks the beginning of Dovecot v2.0. Several things are still missing/broken, but at least I was just able to successfully log in using imap :)

I left v1.3 hg tree there for now, but once v2.0 tree is fully usable I'll just delete the v1.3 tree.

Note the new dovecot-master-example.conf, which you'll need to !include to get the services running. Some settings have also been removed because they're now more generically set in the dovecot-master.conf. I'm thinking that perhaps the config process could still be run in compatibility mode where it's able to use an existing v1.x dovecot.conf and translate the old settings to new settings.