INT 31 P - DPMI 0.9+ - LOCK LINEAR REGION
        AX = 0600h
        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 locked
            AX = error code (DPMI 1.0+) (8013h,8017h,8025h) (see AX=0000h)
Notes:  pages at beginning and end will be locked if the region overlaps them
        may be called multiple times for a given page; the DPMI host keeps a
          lock count for each page
SeeAlso: AX=0601h,INT 21/AX=251Ah,INT 21/AX=EB06h