SpringAMQPExecutorTask stops regardless of error if Endpoint is stopped

* fixes possibly infinite run of task esp. if running inside a container
  (i.e. tomcat or OSGi environment)
Ack in manual mode
Merge remote-tracking branch 'ack-in-manual-mode/ack-in-manual-mode'
Merge pull request #47 from verschdl/master

SpringAMQPExecutorTask stops regardless of error if Endpoint is stopped