INT 31H 000dH: Allocate Specific Descriptor

                                                    Compatibility: DPMI 0.9+ 
 Expects: AX    000dH
          BX    selector
 Returns: CF    NC (clear) if successful; else AX = DPMI Error Code
          AX    ?selector of allocated descriptor?
    Info: This allocates one of the first 16 entries in the LDT.  Selector
          values 04H-7cH are reserved for this purpose.

    Note: The DPMI spec does not identify AX as a return value; so I'm
          guessing here.  Also, It's not clear why you would want to
          allocate one of these puppies (perhaps to make, say, 0040H work
          as a descriptor to 0040:0000).

See Also: DPMI API
          INT 2fH: Multiplex Interrupt
          DOS Functions