Add variable to makefile for selecting which BFS to use.
Add variable to makefile for selecting which BFS to use.

(default is bfs with public tasks and using barriers)

uwsampa/grappa,buaasun/grappa,buaasun/grappa,uwsampa/grappa,buaasun/grappa,alexfrolov/grappa,uwsampa/grappa,alexfrolov/grappa,buaasun/grappa,uwsampa/grappa,buaasun/grappa,uwsampa/grappa,alexfrolov/grappa,uwsampa/grappa,alexfrolov/grappa,buaasun/grappa,alexfrolov/grappa,alexfrolov/grappa,buaasun/grappa,uwsampa/grappa,alexfrolov/grappa