Changes to web flow action proposal

[Brent Putman]

Aside from the subtleties of the handling choices:  Don't forget about java.lang Error, the other
type of unchecked, undeclared thing that can be thrown.  So perhaps some or all of the catching
should be for java.lang.Throwable, which handles both RuntimeException and Error cases.

I didn't get a chance to say on the call, but whatever it winds up looking like, I agreed with
Scott's comment that the same doPre/do/doPost pattern ought to be used in MessageHandlers as well,
at least for ones that have any kind of state, etc.  I guess for both handlers and actions, ones
that are simple and stateless don't necessarily need that pattern.  But also wouldn't hurt to just
make them all consistent.