* changes mutt_buffy_check to only poll the selected folder when it
  is opened, not all mailboxes (unless the timeout has expired).
  This is a noticeable win if you have a few IMAP mailboxes.

* sets the default checkinterval to 60 seconds from 0. Things are
  much much slower with 0.

* makes some cosmetic renames

* moves lots of generic imap stuff into a separate file, imap/util.c

* abstracts the process of sending a command to an IMAP server a bit
  better (lots more to do here, though).

* moves the message-set creation code used by the new fastdelete
  code into its own function, since it is generally useful.

* implements server-side copy of messages. Tagged messages are
  copied in one command, thanks to the message-set function. Speedy!

(From: Brendan Cully; modifications by tlr.)