Streamline saving in the ChangeRecorder.

Before: ChangeRecorderTest::testChangeRecorder was saving 10 times
(0, 2, 2, 2, 1, 1, 0, 0, 0, 0)
After: ChangeRecorderTest::testChangeRecorder is saving 4 times, i.e.
only when something really changed in pendingNotifications:
(0, 2, 1, 0)