MetaBox::the_value() - Added (BC Safe) $return parameter

I have added a second argument to the MetaBox::the_value() method.

The signature now looks like:
function the_value($n = NULL, $return = false)

The $return parameter functions the same way it would for print_r().  If $return is true, the output is returned instead of echoed.

Case in point - I need to run the output through Wordpress' apply_filters() function.  Without this, I had to buffer the output like this:

```php
    ob_start();
    $metabox->the_value($n);
    echo apply_filters('the_content', ob_get_clean());
```

After the change:

```php
    echo apply_filters('the_content', $metabox->the_value($n, true);
```