Fixed 32-bit windows bug in rigid_body_tree_test.cc.
Fixed 32-bit windows bug in rigid_body_tree_test.cc.

billhoffman/drake,billhoffman/drake,billhoffman/drake,billhoffman/drake,sheim/drake,billhoffman/drake,billhoffman/drake,billhoffman/drake,sheim/drake,sheim/drake,sheim/drake,sheim/drake,sheim/drake,sheim/drake,sheim/drake,billhoffman/drake