Fix handling of PID file.
Fix handling of PID file.

vishnuvaradaraj/redwood,andybalholm/redwood,unixabg/redwood,andybalholm/redwood,unixabg/redwood,yinheli/redwood-filter,vishnuvaradaraj/redwood,vishnuvaradaraj/redwood,yinheli/redwood-filter,yinheli/redwood-filter