Element _CURRENTEVENTHANDLER is undefined in VARIABLES.

[joe.rinehart]

After the changes to event handler queueing/dequeuing for onRequestStart result events, the _currentEventHandler member of EventRequest? isn't set when onRequestStart runs.

This is a bit of a problem to fix - it'd be easy to queue/dequeue the ModelGlue?.* event handlers, but that'd mean ModelGlue?.onRequestStart would be the result of arguments.event.getEventHandlerName(), which'd break most existing uses of it.

To fix it, implement an "initialEventHandler" member of EventRequest? - reflect its name during onRequestStart, and the name of the last event handler run during onQueueComplete and onRequestEnd, making the API work just like the 1.1 API.

[joe.rinehart]

(In [260]) Fixes #239