Add "www." to URL string
<p>I need to check a URL string, and if the URL does not contain "www.", insert it in the correct position.</p>

<p>For example, the strings on the left should be transformed as indicated:</p>

<pre class="lang-none prettyprint-override"><code>www.myweb.com        =&gt; www.myweb.com
myweb.com            =&gt; www.myweb.com
http://myweb.com     =&gt; http://www.myweb.com or www.myweb.com
http://www.myweb.com =&gt; http://www.myweb.com or www.myweb.com
</code></pre>
