added plug-in APIs for folder view.
put vbox on the top of folder view.
properly count the number of new messages on local and remote mailboxes.
reflect display_folder_unread setting immediately.
added an option to update only INBOX on checking new messages of IMAP4 accounts.
modified the display of folder view.
fixed selection becoming wrong when another folder was clicked quickly.
implemented folder move.
expand parent folder when new one is created.
modified the way to revert selection after menu popup.
fixed a bug that caused crash if FolderView::selected is NULL.
implemented message-to-folder DnD.
reimplemented folder view with GtkTreeView.
Initial import of Sylpheed (GTK2 version).