XMS 11H: Release Upper Memory Block

                                                     Compatibility: XMS 2.0+ 
 Expects: AH    11H
          DX    segment address of he UMB (as obtained via XMS 10H)
 Returns: AX    status: 0000H = successful
                        0001H = error and BL=XMS error code (if BL >= 80H)
    Info: This frees ownership of a UMB obtained via XMS 10H (request UMB).

          See Accessing Upper Memory for the correct (DOS-blessed) way to
          get and release a UMB when running DOS 3.0+.

   Notes: When a UMB has been released, any code and data in it becomes
          invalid and should not be accessed.

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