Join two or more arrays of arrays
<p>Suppose I have two arrays like the following:</p>

<pre><code>$arr2 = array(array("first", "second"), array("third", "fourth"));
$arr3 = array(array("fifth", "sixth", "seventh"), array("eighth", "ninth"), array("tenth", "eleventh"));
</code></pre>

<p>And I want a result like this: </p>

<pre><code>$arr4 =  array("first", "second", "third", "fourth", "fifth", "sixth", "seventh","eighth", "ninth","tenth", "eleventh" );
</code></pre>

<p>How to do that? in PHP</p>
