I should be used in all ops in the new backend.  I made a sweep to make sure they all used it a while ago. It seems that code disappeared somewhere though, since I can't find it either.  It is currently safe to not do this, but I plan to used fully asynchronous streams in gpuarray so we would get weird and hard to debug problems if we don't do this.  We could also just properly port these ops which will use the correct stream automatically.

For now, though I guess it's fine without it.