isatty
======

POSIX specification:
 http://www.opengroup.org/onlinepubs/9699919799/functions/isatty.html

Gnulib module: isatty

Portability problems fixed by Gnulib:

  * On native Windows, this function also returns true for character devices such as NUL.

  * This function crashes when invoked with invalid arguments on some platforms: MSVC 9.

Portability problems not fixed by Gnulib: