Update iwxxmd.py to gracefully recover when observer object dies

[mgoberfield]

Not so much a bug with iwxxmd.py code as a need to gracefully recover when python's Watchdog observer quits responding to events in the monitored directory.

Steps to reproduce the behavior:
Difficult to reproduce the issue but seems most likely to occur when there is rapid influx of new files (100+ files within a few minutes), but not always. I've found monitoring to run fine for weeks and then suddenly fail. Other times, the observer will fail after a few hours during quiescent times.

Watchdog module has a Observer is_alive() method to determine if the observer is okay. iwxxmd.py will be updated to use this and 'do the right thing' when the current observer stops working.

• OS: Linux