Fix for issue #1279 - Add .Request property to ApiController

This change adds a .Request property to the ApiController class that can
be used to access an HttpRequestMessage wrapping the HttpContext.

The HttpRequestMessage is stored in an http feature to make it accessible
to model binders and other infrastructure.
Thanks that's good to know. They went to great lengths in WebAPI to dispose the HReqM because they exposed the ability to register objects for disposal http://msdn.microsoft.com/en-us/library/system.net.http.httprequestmessageextensions.registerfordispose(v=vs.118).aspx

The framework even uses this in a few places.


The rub here is that we **might** bring back this feature for the shim. If we can easily and simply provide a lifetime guarantee using the feature collection then it seems worth doing right now. So is it supposed to do that?