message: actually freeing memory in buffer manager
diff: @@ -92,6 +92,8 @@ void BufferManager::Unpin(block_id_t block_id) {
  assert(buffer_entry->ref_count > 0);
  buffer_entry->ref_count--;
  if (buffer_entry->ref_count == 0) {
  + // no references left: move block out of used list and into lru list
  + auto entry = used_list.Erase(buffer_entry);
  if (buffer_entry->buffer->type == FileBufferType::MANAGED_BUFFER) {
  auto managed = (ManagedBuffer *)buffer_entry->buffer.get();
  if (managed->can_destroy) {
  @@ -101,8 +103,6 @@ void BufferManager::Unpin(block_id_t block_id) {
  return;
  }
  }
  - // no references left: move block out of used list and into lru list
  - auto entry = used_list.Erase(buffer_entry);
  lru.Append(move(entry));
  }
  }
  