Add support for caching of events queued via results

[cfgrok]

At the present time the implementation of event-handler caching does not support the caching of events that are queued using a <result> tag, only top-level events initiated by the user. The event caching mechanism should be refactored to allow for caching of queued events, as this would allow discrete portions of rendered pages to be individually cached.

[boomfish]

Closed #380 as a duplicate of this ticket.