Updated swift to version 4.3.1 (fixes error with PHP5.5), add login when plugin failure occurs

Updated swift library to version 4.3.1 to fix the following error in PHP5.5

```
<b>Notice</b> (8)</a>: Undefined property: Swift_Transport_StreamBuffer::$_sequence [<b>APP/plugins/email/vendors/swift/lib/classes/Swift/Transport/StreamBuffer.php</b>, line <b>211</b>]
```