Synch with Gnus trunk.

Synch with Gnus trunk.
2009-09-10  Teodor Zlatanov  <tzz@lifelogs.com>

 * net/imap.el (imap-interactive-login): Better messages.
 (imap-open): Fix bug with renamed buffer on reconnect.
 (imap-authenticate): Add buffer-local imap-last-authenticator variable
 for easier debugging and cleaner code.  On successful (guessed based on
 server capabilities) secondary authentication, set imap-state
 correctly.
 (imap-last-authenticator): Define imap-last-authenticator as a variable
 to avoid warnings.