Eli Zaretskii wrote:
>> +  return isatty (fd) - 1;
> Do we need this "-1" part now?  It could misfire if isatty does
> return 1 some day.

Sorry, I don't so how it can misfire.  isatty returns 1 on success, 0 on 
failure; whereas the caller returns 0 on success, -1 on failure.  So 
subtracting 1 is the right thing to do, no?

A revised patch, taking your other comments into account, is attached. 
It's relative to trunk bzr 117527.