Get Vendor-Specific API Entry Point

Returns an address which can be called to use host-specific
extensions to the standard set of DPMI functions.  DPMI 1.0
clients should avoid use of this function (see Note).

Call With:

   AX     = 0A00H
   DS:(E)SI= selector:offset of ASCIIZ (null-terminated)
           string which identifies the DPMI host vendor

Returns:

   if function successful
   Carry flag= clear
   ES:(E)DI= selector:offset of extended API entry point

   and DS, FS, GS, EAX, EBX, ECX, EDX, ESI, and EBP may be
           modified.
   if function unsuccessful
   Carry flag= set
   AX     = error code
           8001H   unsupported function (extension not
                   found)

Notes:

o  The null-terminated string specifies the host-specific
   vendor name or some other unique identifier to obtain a
   specific extension entry point.  The string comparison
   used to look up the API entry point is case-sensitive.
o  Clients must use a FAR CALL to reach the extended API
   entry point.
o  All extended API parameters are specified by the vendor.
o  DPMI 1.0 clients should use Int 2FH Fn 168AH in
   preference to this function.  DPMI 1.0 hosts support this
   function solely for backward compatibility with DPMI 0.9
   clients.