INT 31 P - DPMI 0.9+ - UNLOCK LINEAR REGION
        AX = 0601h
        BX:CX = starting linear address
        SI:DI = size of region in bytes
Return: CF clear if successful
        CF set on error
            none of the memory is unlocked
            AX = error code (DPMI 1.0+) (8002h,8025h) (see AX=0000h)
Notes:  pages at beginning and end will be unlocked if the region overlaps them
        memory whose lock count has not reached zero remains locked
SeeAlso: AX=0600h,INT 21/AX=251Bh,INT 21/AX=EB07h