folder.IMAP: Improve dropped connection handling in quickchanged()
folder.IMAP: Improve dropped connection handling in quickchanged()

The quickchanged() function was not handling dropped connections yet. If
IMAP4.select() throws a FOLDER_RETRY error, we will now discard the
connection, reconnect and retry.

Signed-off-by: Sebastian Spaeth <98dcb2717ddae152d5b359c6ea97e4fe34a29d4c@SSpaeth.de>
Signed-off-by: Nicolas Sebrecht <347709267ddd1958560c4c317ea3fd613f10a719@laposte.net>

frioux/offlineimap,frioux/offlineimap