Clean up polling_observer.py and enable subclasses to inherit from PollingObserver.
Clean up polling_observer.py and enable subclasses to inherit from PollingObserver.

Signed-off-by: unknown <a980e82c42f5ced04f1410d7997ae1829d09f5da@.(none)>

glorizen/watchdog,mconstantin/watchdog,edevil/watchdog,ymero/watchdog,ymero/watchdog,javrasya/watchdog,teleyinex/watchdog,javrasya/watchdog,glorizen/watchdog,edevil/watchdog,mconstantin/watchdog,javrasya/watchdog,edevil/watchdog,ymero/watchdog,teleyinex/watchdog,gorakhargosh/watchdog,glorizen/watchdog,teleyinex/watchdog,edevil/watchdog,edevil/watchdog,gorakhargosh/watchdog,mconstantin/watchdog