error prone jquery extending
<p>Anybody familiar with patterns for:</p>

<ul>
<li>Checking for existing jQuery extension most safely? </li>
<li>And how to exit    from it safely if code can not be executed.</li>
</ul>

<p>Like </p>

<pre><code>(function($){
    if (jQuery.fn.pluginName)
    ......
    }
})(jQuery);
</code></pre>

<p>10x, BR</p>
