In-memory snapshots work both with fswebcam and raspistill.
If the test images are different, snap a high-res photo
stamped with date and time.
Save it to a remotely mounted filesystem if possible,
but fall back to a local filesystem in case the net goes down.
- Much better handling of in-memory snapshots
  that don't touch disk at all.
- If changed, snap a high-res image; save it to a remotely
  mounted dir if possible, else fall back to a local dir.
- In gmotion_detect, allow mouse drags to reset the hot zone
  (unfortunately doesn't work on RPi yet due to latency and
  event handling issues).
- Lots of other reliability fixes.