force recompiling of regex where closures matter

force recompiling of regex where closures matter

There are some cases where on the second run of a run-time regex, the
text of the pattern hasn't changed, but we should still recompile to
ensure that closure behaviour is correct.

These cases are:

1) run-time code:

    my $code = '(??{$x})';
    for my $x (1..3) {
        $x =~ /$code/; # recompile to see fresh value of $x
    }

2) embedded regexes with code:

    for my $x (1..3) {
	my $r = qr/(??{$x})/;
        "A$x" =~ /A$r/; # recompile to see new $r
    }

With this fix, all the TODO tests in re/pat_re_eval.t now pass. (Note that
a couple of those TODO tests were actually broken and are fixed in this
commit)