streamwriter doesn't stop writing until a frame is written

[Jared R. Males]

this happens if, say, we are recording dm02disp08 for iEFC, then stop iEFC, and so there will be no more writes to dm0disp08.

note this is the intended behavior for a streaming science camera, as we are trying to be conservative and save the current exposing frame, but for an intermittent stream like a dm it means long hangs.

Maybe the right thing is really to throw away the current exposure in all cases -- the user probably doesn't want the current frame if they stopped recording in the middle of it.

[Jared R. Males]

76f24f1