As of "Win32: Thread-safe windows console output", child processes may
print to the console even if stdout has been redirected to a file. E.g.:
git config tar.cat.command "cat"
git archive -o test.cat HEAD
Detecting whether stdout / stderr point to our console pipe is currently
based on the assumption that OS HANDLE values are never reused. This is
apparently not true if stdout / stderr is replaced via dup2() (as in
builtin/archive.c:17).
Instead of comparing handle values, check if the file descriptor isatty()
backed by a pipe OS handle. This is only possible by swapping the handles
in MSVCRT's internal data structures, as we do in winansi_init().
Reported-by: Johannes Sixt <j6t@kdbg.org> Signed-off-by: Karsten Blees <blees@dcon.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>