Get Real Mode Interrupt Vector

Returns the contents of the current virtual machine's real
mode interrupt vector for the specified interrupt.

Call With:

   AX     = 0200H
   BL     = interrupt number

Returns:

   Carry flag= clear (this function always succeeds)
   CX:DX  = segment:offset of real mode interrupt handler

Notes:

o  The value returned in CX is a real mode segment address,
   not a selector.  Attempts to place this value into a
   segment register in protected mode may cause a general
   protection (GP) fault.
o  All 100H (256) real mode interrupt vectors must be made
   available through this function by the DPMI host.