* Use raw file descriptor in posix_isatty() check to avoid warning on

* Use raw file descriptor in posix_isatty() check to avoid warning on
  Linux systems with at least some versions of PHP

For some reason posix_isatty(STDIN) prints a warning on Linux about being unable to seek, though it gives the right return value and has no obvious ill effects otherwise.
No such warning appears on Mac OS X.
Using the raw file descriptor number (0 for stdin) seems to work, and is already used in the parser test framework where it checks stdout (1) this way.