[#2643] Throw TooLongFrameException instead of using fireExceptionCaught

Motivation:

It's not always the case that there is another handler in the pipeline that will intercept the exceptionCaught event because sometimes users just sub-class. In this case the exception will just hit the end of the pipeline.

Modification:
Throw the TooLongFrameException so that sub-classes can handle it in the exceptionCaught(...) method directly.

Result:
Sub-classes can correctly handle the exception,