Takes two Ctrl + C presses to shut down the server

When running gunicorn, I can stop it with Ctrl + C and it looks like it's shutting down cleanly - the BaseCamera worker thread exists, then it says "Clearing /home/pi/micrographs/tmp..." and appears to hang. Pressing Ctrl + C again kills it properly; is the thread that it's waiting on hung? I think if I close the web browser window it does then terminate, but not before then; maybe we need a way to kill the MJPEG stream?