Replace boost::function with std::function (C++11)

Zcash: Only applied changes to src/bench/

src/bench/bench.cpp

@@ -5,6 +5,7 @@
 #include "bench.h"
 #include "perf.h"
 
+#include <assert.h>
 #include <iostream>
 #include <iomanip>
 #include <sys/time.h>

src/bench/bench.h

@@ -5,10 +5,11 @@
 #ifndef BITCOIN_BENCH_BENCH_H
 #define BITCOIN_BENCH_BENCH_H
 
+#include <functional>
+#include <limits>
 #include <map>
 #include <string>
 
-#include <boost/function.hpp>
 #include <boost/preprocessor/cat.hpp>
 #include <boost/preprocessor/stringize.hpp>
 
@@ -59,7 +60,7 @@ namespace benchmark {
         bool KeepRunning();
     };
 
-    typedef boost::function<void(State&)> BenchFunction;
+    typedef std::function<void(State&)> BenchFunction;
 
     class BenchRunner
     {