message: Add missing ConstTableRef::operator!=
diff: @@ -56,6 +56,11 @@ public:
  return m_table == other.m_table && m_instance_version == other.m_instance_version;
  }
  + bool operator!=(const ConstTableRef& other) const
  + {
  + return !(*this == other);
  + }
  +
  std::ostream& print(std::ostream& o) const
  {
  return o << "TableRef(" << m_table << ", " << m_instance_version << ")";
  