fix thread ID to be displayed on OS X (fix #874)
fix thread ID to be displayed on OS X (fix #874)

rimms/jubatus,roselleebarle04/jubatus,gintenlabo/jubatus,jubatus/jubatus,gintenlabo/jubatus,jubatus/jubatus,roselleebarle04/jubatus,jubatus/jubatus,elkingtonmcb/jubatus,rimms/jubatus,elkingtonmcb/jubatus,mathn/jubatus,mathn/jubatus