Issue #592 - ActionResult is not being executed by ResultFilterAttribute

The issue here is actually different than described in the bug.
ResultFilter should only short circuit when .Cancel is set to true. This
is consistent with legacy MVC.

Added tests for all of this stuff. There's already good test coverage for
the invoker, what was missing was coverage for the attributes and for the
methods on Controller. ExceptionFilterAttribute and
AuthorizationFilterAttribute don't have short circuiting logic inside of
them, so they are already covered by tests for the invoker.
This seemed like the best way to share test code between these three sets of tests. Anyone have a better suggestion?