bind: Convert lost qualifier

[Yuan Yao <yaoyuan1216@…>]

The following code doesn't compile with vs2013. It will be OK if boost::bind is replaced with std::bind or using less placeholders.

#include <boost/bind.hpp>
void foo(int&, int, int){}

int main(){
	using boost::bind;	

	int a;
	auto&& f = bind(&foo, _1, _2, _3);
	f(a, 0, 0);
	
	return 0;
}