INT 31 P - DPMI 0.9+ - UNLOCK SELECTOR
        AX = 0005h
        BX = selector to unlock (permit paging)
Return: ???
Note:   although marked as reserved in versions 0.9 and 1.0 of the DPMI
          specification, this function is called by MS Windows TASKMAN,
          PROGMAN, and KERNEL
SeeAlso: AX=0601h