Throw an OfflineImapError when SELECTing a folder is unsuccessful and
bail out with a FOLDER serverity. In accounts.py catch all
OfflineImapErrors and either just log the error and skip the folder or
bubble it up if it's severe.
Signed-off-by: Sebastian Spaeth <Sebastian@SSpaeth.de>
Signed-off-by: Nicolas Sebrecht <nicolas.s-dev@laposte.net>