Add missing <cassert> headers

bench/bench_alloc_expand_bwd.cpp

@@ -19,6 +19,7 @@
 #include <boost/container/vector.hpp>
 #include <memory>    //std::allocator
 #include <iostream>  //std::cout, std::endl
+#include <cassert>   //assert
 
 #include <boost/timer/timer.hpp>
 using boost::timer::cpu_timer;