More updates to the async error handling triggered by kkolinko's review

      - simplify check to see if listeners changed async state during onTimeout
- add option to control if onError fires during error handling (it doesn't if called from the timeout code since that has its own event)
- add check to see if listeners changed state during onError
- add check to see if state changed during "error dispatch"
- remove AsyncState.ERROR as a valid start state for asyncPostProcess()
- aligned the unit tests (one change) with the new behaviour

Not tested with the TCK.

git-svn-id: https://svn.apache.org/repos/asf/tomcat/trunk@1409030 13f79535-47bb-0310-9956-ffa450edef68