XMS 09H: Allocate Extended Memory Block

                                                     Compatibility: XMS 2.0+ 
 Expects: AH    09H
          DX    desired size of block, in K-bytes
 Returns: AX    status: 0000H = successful
                        0001H = error and BL=XMS error code (if BL >= 80H)
          DX    XMS handle
    Info: This allocates a block of extended memory and returns a handle to
          use in future reference to that block.

          If no memory is allocated, DX returns with 0000H (null handle).

          By default, XMS supports 32 handles.  Use HIMEM.SYS /NUMHANDLES=
          in the DEVICE= CONFIG.SYS command to increase this max.

See Also: XMS Functions
          Extended Memory Specification (XMS)
          DOS Functions