Raise exception if monitor thread died unexpectedly when refreshing (likely because of forking)
Compatibility fix: use isAlive instead of is_alive for python < 2.6
Merge branch 'pr/190'

* pr/190:
  Compatibility fix: use isAlive instead of is_alive for python < 2.6
  Raise exception if monitor thread died unexpectedly when refreshing (likely because of forking)
Add Xiuming Chen to contributors.
Test that schedule_refresh asserts if monitor thread is gone.
Raise InvalidOperation if monitor thread is dead.
Dead code.