Compatibility: 4.0+
Expects: AX    b711H
                                                                  
Returns: CF    Carry Flag clear (NC) if no error
                                                                  
Info: This is an oddball.  When you call this fn, it sets a one-shot
APPEND internal flag which affects what happens on the next call
to any of:

3dH    (open file via handle)
4300H  (get file attribute)
4eH    (find file)
6cH    (extended file open/create)

Each of these DOS fns require an ASCIIZ  filespec as a parameter.
When the Truename flag is set, APPEND overwrites the input
parameter with the full and actual name of the file.  It then
resets the internal Truename flag.

You must be sure to that the filespec parameter you pass to those
DOS fns has plenty of unused space at the end.  APPEND may expand
that filespec to as large as 79 bytes (a 2-byte d:, 64-byte
\path, and a 12-character filename.ext and a terminating byte of
00H.

Notes: This service is available only if APPEND.EXE is loaded.  If you
just want a flexible way to obtain a fully-qualified
d:\path\filename.exe (given an ambiguous or partial filename),
you might try using the undocumented DOS Fn 60H: Query TrueName.

- -

INT 2fH b711H: Set APPEND.EXE Truename Flag