Get/set global code page table (INT 21h, 66h)

        Entry:
          AH = 66h
          AL = 00h get global code page
             = 01h set global page
        Return:
          CF = 1
               AX = error code if carry flag set
          CF = 0
               If AL=00h
                 BX = active code page
                 DX = system code page
               If AL=01h
                 BX = active code page
                       437  US
                       850  Multilanguage
                       860  Portugal
                       863  Canada (French)
                       865  Norway/Denmark
                 DX = system code page (active page at boot time)