[jsr-314-open] Adding a description field to the JavaScript event payload

[Jim Driscoll]

I'd like to propose that we add a freeform text description field to the 
JavaScript event and error payload.

This would allow for user readable descriptions to go along with errors 
like the infamous "MalformedXML" error.

I think this could fit into an errata, since:
1) It's got no backward incompatibility impact.
2) It's a single line in the spec.
3) It's (almost) trivial to implement.

and most importantly:
4) We really should have had this in there in the first place, and it's 
omission was really more of an oversight than a deliberate choice.

Thoughts?

I've opened up spec issue 570 to track this:
https://javaserverfaces-spec-public.dev.java.net/issues/show_bug.cgi?id=570

And yes, I made it a P1.

Jim