Sqs poll coroutine fix

The polling routine had a method exit that did not set the result, which would be invoked if the object had been disposed. In addition, the scheduling of poll had a race condition where it might re-activate the poll timer after disposal, which then would cause repeated coroutine "result not set" warnings in the log.

In addition, log4net was set to explicitly copy to the output dir, since its presence in the GAC would otherwise cause the msbuild script fail