1089: Exception inside PushStreamContent won't be caught by
ExceptionFilterAttribute

Adding overloads for async onStreamAvailable handlers. Aslo, getting rid
of the whole CompleteTaskOnCloseStream. The task is complete either if you
return from your sync OnStreamAvailable handler or when the task that you
return from you async OnStreamAvailable handler completes.

Also, note that adding the overloads is potentaillay a compile time
breaking change due to the way method group overload resolutions work.
http://stackoverflow.com/questions/2057146/compiler-ambiguous-invocation-error-anonymous-method-and-method-group-with-fun
fix build break.

missing </summary> tag in xml comment.
Fix {action} with attribute routing.
https://aspnetwebstack.codeplex.com/workitem/1239
ApiControllerActionSelector's GetActionMapping should not return action descriptors for NonAction decorated methods.
https://aspnetwebstack.codeplex.com/workitem/1220