v4Allow TTY tests to run under recent Mac OS

> TTY tests were previously skipped on all Mac OS systems because of a
> bug where reading from pty master occasionally hung. This bug has since
> been found not to be reproducible under Mac OS 10.9 and 10.10.1.
>
> Therefore, run TTY tests under Mac OS 10.9 (Mavericks) and higher.
>
> Signed-off-by: Mike Blume <blume.mike@gmail.com>
> Improved-by: Junio C Hamano <gitster@pobox.com>
> Signed-off-by: Junio C Hamano <gitster@pobox.com>
> Improved-by: John Szakmeister <john@szakmeister.net>
> Improved-by: Johannes Sixt <j6t@kdbg.org>
> Improved-by: Jeff King <peff@peff.net>
> ---

>  t/lib-terminal.sh | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/t/lib-terminal.sh b/t/lib-terminal.sh
> index 5184549..275fb09 100644
> --- a/t/lib-terminal.sh
> +++ b/t/lib-terminal.sh
> @@ -29,7 +29,12 @@ test_lazy_prereq TTY '
>  	# After 2000 iterations or so it hangs.
>  	# https://rt.cpan.org/Ticket/Display.html?id=65692
>  	#
> -	test "$(uname -s)" != Darwin &&
> +	# Under Mac OS X 10.9, this problem appears to be gone.
> +	#
> +	{
> +		test "$(uname -s)" != Darwin ||
> +		test "$(uname -r | cut -d. -f1)" -ge 13
> +	} &&
>  
>  	perl "$TEST_DIRECTORY"/test-terminal.perl \
>  		sh -c "test -t 1 && test -t 2"

> TTY tests were previously skipped on all Mac OS systems because of a
> bug where reading from pty master occasionally hung. This bug has since
> been found not to be reproducible under Mac OS 10.9 and 10.10.1.
>
> Therefore, run TTY tests under Mac OS 10.9 (Mavericks) and higher.

> Hi,
>
> Mike Blume wrote:
>
>> TTY tests were previously skipped on all Mac OS systems because of a
>> bug where reading from pty master occasionally hung. This bug has since
>> been found not to be reproducible under Mac OS 10.9 and 10.10.1.
>>
>> Therefore, run TTY tests under Mac OS 10.9 (Mavericks) and higher.
>
> *puzzled* Testing on Yosemite with the following script[1]
>
>         perl -MIO::Pty -MFile::Copy -e '
>                for (my $i = 0;; $i++) {
>                        my $master = new IO::Pty;
>                        my $slave = $master->slave;
>                        if (fork == 0) {
>                                close $master or die "close: $!";
>                                open STDOUT, ">&", $slave or die "dup2: $!";
>                                close $slave or die "close: $!";
>                                exec("echo", "hi", $i) or die "exec: $!";
>                        }
>                        close $slave or die "close: $!";
>                        copy($master, \*STDOUT) or die "copy: $!";
>                        close $master or die "close: $!";
>                        wait;
>                }
>         '
>
> still seems to hang eventually (after 61 iterations when my officemate
> tried it), reproducing the bug.
>
> Do you get a different result?

> The bug was originally found in an autobuilder that would run the test
> suite when new versions were pushed to check for regressions.  Even if
> the hang only happened 0.1% of the time, that would get the
> autobuilder stuck after a while, which was how the problem got
> noticed.