Incorporate code review feedback.
Issue 1041: parse errors in OData $filter and $orderby are not sent back
to the client properly
Issue 1302: MediaTypeFormatter's WriteToStreamAsync overload taking in
CancellationToken not being invoked

HttpContent.SerializeToStreamAsync doesn't take in a CancellationToken.
So, there is no easy way to get the CancellationToken to the formatter
while writing response. We are cheating here by passing fake cancellation
tokens. We should fix this when we fix HttpContent.
Issue 1324:  Delta<T>.Patch doesn't perform validation on the entity

Adding a helper method on the ODataController to perform validation
after the delta has been applied.