message: core: Expose Comm encapsulation outside ADIOS factory
  For now it has an implicit conversion to MPI_Comm anyway.
diff: @@ -40,7 +40,7 @@ public:
  const bool m_DebugMode = true;
  /** Get the communicator passed to constructor for parallel case. */
  - MPI_Comm GetComm() const { return m_Comm; }
  + helper::Comm const &GetComm() const { return m_Comm; }
  /** Changed by language bindings in constructor */
  const std::string m_HostLanguage = "C++";
  