[ros-diffs] [ion] 25483: - Start partial implementation of Executive Lightweight Callbacks: ExAllocateCallBack, ExInitializeCallBack, ExFreeCallBack, ExWaitForCallBacks, ExGetCallBackBlockRoutine, ExGetcallBackBlockContext, ExDoCallBack. - Stub ExReferenceCallBackBlock and ExDereferenceCallBackBlock until I get the locking right. - These callbacks are used by Cm as well as Ps inside Windows NT and combine the power of PushLocks, Rundown Protection and Fast Referencing to ensure callbacks only get called onc