Based on !2524.
This adds the remaining stubs needed for Crazy Machines 3 to work and decode preview images correctly in online mode.
-- v3: msvcr110: Implement _Context::_IsSynchronouslyBlocked. msvcr110: Add _Context::_IsSynchronouslyBlocked stub. msvcr110: Add _Cancellation_beacon::_Cancellation_beacon_dtor stub. msvcr110: Add _Cancellation_beacon::_Cancellation_beacon_ctor stub.