Called in main thread whenever a message is received from another thread
virtual void ProcessAsyncMessage( CXllMtMsg* msg = NULL );
A message class descended from CXllMtMsg. This is the value passed as an argument to PostMessage()
This virtual function must be implemented by any class descended from CXllPushApp.
ProcessAsyncMessage() is called whenever a messsage is received from another thread, at a time when it is safe for the add-in to process the message. The implementation should process or store the message, and pass a notification of any changes to the push engine, using CXllPush::UpdateCells().