For EventsRegisterTest that test updates to streams and
subscriptions, we now validate the events generated by
the actions under test conform to predicted schemas.
We define the schemas with help from the validators code
that is also sometimes used to validate incoming request
parameters for our views.
(imported from commit b4222b920a588e15cccee4a2349c074ca9697448)
This sets up a scheme to validate complex data structures and
give specific error messages for improperly typed parameters.
(imported from commit 33b2f070d993da4ee929119dd41503bd0128c8eb)
Steve Howell