Require at least Time::HiRes 1.9716 for a functional alarm()

1.9715's alarm() is non-functional on at least some systems, evidenced
by various CPAN testers failure reports from vanilla Perl 5.8.9 installs
which include 1.9715 in core.

The functionality of alarm() may be tested like so:

    perl -MTime::HiRes=alarm -le '
        $SIG{ALRM} = sub { print "alarm: ", time; die "alarm works\n" };
        alarm 1;
        print "start: ", $start = time;
        'spin' while $start + 4 > time;
        die "alarm broken\n";
    '
Releng for 0.95