buffer: require a move constructor to avoid copies

remove unneded copy constructors from several classes

src/util/buffer.h

@@ -21,7 +21,7 @@ Revision History:
 --*/
 #pragma once
 
-#include<string.h>
+#include <type_traits>
 #include "util/memory_manager.h"
 
 template<typename T, bool CallDestructors=true, unsigned INITIAL_SIZE=16>
@@ -39,6 +39,7 @@ protected:
     }
 
     void expand() {
+        static_assert(std::is_nothrow_move_constructible<T>::value);
         unsigned new_capacity = m_capacity << 1;
         T * new_buffer        = reinterpret_cast<T*>(memory::allocate(sizeof(T) * new_capacity));
         for (unsigned i = 0; i < m_pos; ++i) {