Add const reference: refs #787
Add const reference: refs #787

Asuka52/jubatus,elkingtonmcb/jubatus,mathn/jubatus,mathn/jubatus,kmaehashi/jubatus,rimms/jubatus,roselleebarle04/jubatus,Asuka52/jubatus,jubatus/jubatus,jubatus/jubatus,gintenlabo/jubatus,roselleebarle04/jubatus,gintenlabo/jubatus,rimms/jubatus,jubatus/jubatus,kmaehashi/jubatus,elkingtonmcb/jubatus