Support running under NSSM

[judwhite]

If the binary isn't running under Service Control Manager (SCM), then StartServiceCtrlDispatcher() will fail with ERROR_FAILED_SERVICE_CONTROLLER_CONNECT. This is a more reliable way of detecting if a service is running under SCM than checking svc.IsAnInteractiveSession. Checking the IsAnInteractiveSession value first can be an optimization to avoid skipping the StartServiceCtrlDispatcher error check.

In Go, svc.Run should fail here calling windows.StartServiceCtrlDispatcher.

Troubleshooting tips, if needed: http://stackoverflow.com/a/30719534 (from 2015-05-26)

[judwhite]

This may be resolved by 8134bf0, needs investigation