Int 2F Fn 1211  U - Dos 3.0+ Internal - Normalize Asciz Filename           [D]

   AX = 1211h
   DS:SI -> ASCIZ filename to normalize
   ES:DI -> buffer for normalized filename

Return: destination buffer filled with uppercase filename, with slashes turned
   to backslashes

See Also: AX=121Eh,AX=1221h