message: ignore unknown headers (a quick and dirty workaround)
  try to address:
diff: @@ -1358,7 +1358,6 @@ public:
  if ( prop.name_ == str )
  return prop.type_;
  }
  - if ( str.find( "X-", 0 ) != std::string::npos )
  return CustomHeader;
  throw std::runtime_error( "headerType: Headername not found" );
  }
  @@ -1368,7 +1367,6 @@ public:
  if ( prop.name_ == headerName )
  return prop.listSeparatorChar_;
  }
  - if ( headerName.find( "X-", 0 ) != std::string::npos )
  return ',';
  throw std::runtime_error( "listSeparatorChar: Headername not found" );
  }
  