[Dovecot] IMAP NOTIFY extension

http://hg.dovecot.org/dovecot-2.2-notify/ contains the initial implementation of IMAP NOTIFY extension. It's less than half-working, but the difficult part of it is done I think. If I give it a command like:

x notify set (personal (messagenew messageexpunge flagchange))

and then in another session I copy a message to another mailbox, it sends:

• STATUS "foobar" (MESSAGES 77 UIDNEXT 78 UIDVALIDITY 1329431281 UNSEEN 75)

This requires mailbox_list_index=yes to work. It works by following the dovecot.list.index.log changes, so it's going to be pretty efficient. Some TODO that I've so far noticed:

• NOTIFY is handled currently only for non-selected mailboxes. (handling the new features for selected mailbox should be simple)
• initial STATUS sending isn't done with STATUS option
• only MessageNew, MessageExpunge and FlagChange notifications are sent currently
• MailboxName handling probably needs to be able to get "old" and "new" views, figure out what changed in them and send those changes (dsync has similar code)
• mailbox list indexes seem to be adding too much stuff, which results in:
• STATUS duplicates, but there should already be code to avoid these so I'm not sure what's going on
• ACLs and shared mailboxes don't work right
• add 0.5s delay before notifying IMAP code, so multiple changes can be bundled into one