message: reactor.Channel: Fix constness error.
diff: @@ -190,7 +190,7 @@ namespace elle
  while (!this->_read_barrier.opened())
  {
  ELLE_TRACE_SCOPE("wait for data");
  - reactor::wait(this->_read_barrier);
  + reactor::wait(elle::unconst(this->_read_barrier));
  }
  ELLE_ASSERT(!this->_queue.empty());
  return details::queue_front(this->_queue);
  