Message handlers and error handling

[Cantor, Scott]

For the record, there are no actions that deliberately throw exceptions
except for the code in AbstractProfileAction that coordinates execution
and throws if the underlying doX methods throw, and a handful of
unimplemented actions that just throw because they're not implemented yet.

So I'm in favor of removing ProfileException (and AuthenticationException,
etc.) from the execute method.

Doesn't solve my handler problem, but it does get rid of an unused feature.

-- Scott