supported PLAIN authentication on IMAP4.
save temporary IMAP4 password. Don't try to connect to IMAP4 server when closing folder.
implemented clearing of IMAP4 message caches on exit.
added an option to update only INBOX on checking new messages of IMAP4 accounts.
enabled custom queue folder.
popup main window when account edit dialog is closed.
fixed focus problem in win32.
separated UI code from prefs_common.c and prefs_account.c.