Bug 826118 - [email/IMAP] Connection loss may not always result in error messages during synchronization, synchronization for the folder will break until app is restarted.
IMAP server jobs need the deathback updated/cleared too.
Add withConnection and resetErrorHandling to imap/folder, to help the use of folderConn in _accessFolderForMutation to be less aware of the actual deathback setting and reseting
Use clearErrorHandler instead of resetErrorHandling