=head2 _save_pwd(sub { ... })

=for category File

Save the current directory and assure that outside the block the old
directory will still be valid.

=cut

sub _save_pwd (&) {
    my $code = shift;
    require Cwd;
    my $pwd = Cwd::cwd();
    eval {
    $code->();
    };
    my $err = $@;
    chdir $pwd or die "Can't chdir back to $pwd: $!";
    die $err if $err;
}