INT 2fH 168AH: Get Vendor-Specific DPMI API Entry Address

                                                    Compatibility: DPMI 0.9+ 
 Expects: AX    168AH
          DS:SI address of ASCIIZ string identifying the vendor
 Returns: AX    0000h = successful
                else  = no such vendor API or not in Protected Mode
          ES:DI vendor-specific API Entry Address
    Info: A DPMI client may use this fn to get an address that will provide
          access to vendor-specific extensions of the DPMI specification.

 DS:(E)SI the string at this address must match exactly with the vendor ID.
          The string comparison is case-sensitive.

 ES:(E)DI on return, this is the address supplied by the vendor.  Access it
          via a FAR CALL.  Registers and other calling conventions are set
          by the vendor.

    Note: You must be in protected mode to call this.

See Also: DPMI API
          INT 2fH 16xxH (Enh386 Windows Services & Notifications)
          INT 2fH: Multiplex Interrupt
          DOS Functions