NAME 
       XorRegionRegion -- Perform 2d XOR operation of one region
                       with second region, leaving result in second region

   SYNOPSIS 
       status = XorRegionRegion(region1,region2)
         d0                        a0      a1

        bool xorregionregion( struct region *, struct region * );

   FUNCTION 
        Join the regions together. If any part of region1 overlaps
        region2 then remove that from the new region.

   INPUTS 
       region1      = pointer to region structure
       region2      = pointer to region structure

   RESULTS
        status - return TRUE if successful operation
                 return FALSE if ran out of memory

   BUGS