Merge branch 'devel-2.1'

* devel-2.1:
  Add asyncnotifier unittests
  Make ConfdInotifyEventHandler a library function
  Comment on AsyncNotifier upstream's availability
  Remove errors.ConfdFatalError
  TestMainloop: test scheduler priorities as well
  Fix race condition in mainloop unittest
  TestMainloop.testReRun
  Add AsyncUDPSocket tests
  Add initial mainloop unittests
  devel/review: make the range argument optional

Signed-off-by: Guido Trotter <ultrotter@google.com>
Reviewed-by: Michael Hanselmann <hansmi@google.com>