This function calls the callback functions for any ACNET Request
Callback Facility messages which have been received since the
previous call. This function is called periodically at non-AST
level by intype for console applications. It is also called by
the shell for Open Access Clients (OACs). Other processes will
have to call this function in their periodic update loops.
This function requires the following include files:
acnet_callback_init, acnet_callback_handle, intype, window_intype