Adding Extensions to an Existing GRADD

When the Video Manager (VMAN) issues the GHI_CMD_INIT command to a GRADD, 
it gives the GRADD a unique ID. Upon return from the GHI_CMD_INIT command, 
the GRADD returns the number of function classes it supports. The GRADD 
must assign a unique GID to each of its function-class instances. The GID 
provided to the GRADD by VMAN must be bumped up by one for every 
function-class instance. 

Note:  For Presentation Manager and Seamless Windows functions, a GRADD 
       must support the Base Function class of services. The GRE2VMAN 
       component looks specifically for a GRADD that supports this class 
       of function. 

 VMAN will allocate one GRADDINFO structure for every class of function 
 that a GRADD supports. VMAN will call VMI_CMD_QUERYCAPS once for every 
 function-class instance. This allows an extension layer to associate a 
 GID with a set of function classes. 

 The extension layer uses the VMI_CMD_EXTENSION function to communicate 
 with a GRADD. It is up to the extension layer to define the unique 
 extension functions. The extensions must use VMAN to communicate with the 
 GRADD. The input packet to the VMI_CMD_EXTENSION function includes 
 information about screen change areas and hardware serialization. This 
 information allows VMAN to maintain hardware pointer support and hardware 
 serialization.