INT 31 P - DPMI 0.9+ - RELOCK REAL MODE REGION
        AX = 0603h
        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 relocked
            AX = error code (DPMI 1.0+) (8002h,8013h,8025h) (see AX=0000h)
Notes:  pages at beginning and end will be relocked if the region overlaps them
        pageability of real mode pages is binary, not a count