Transport status notification.
| aTransport | the transport sending this status notification. |
| aStatus | the transport status (resolvable to a string using nsIErrorService). See nsISocketTransport for socket specific status codes and more comments. |
| aProgress | the amount of data either read or written depending on the value of the status code. this value is relative to aProgressMax. |
| aProgressMax | the maximum amount of data that will be read or written. if unknown, 0xFFFFFFFF will be passed. |