Description:
------------
The code highlight functions always output a surrounding <span> element 
to make all the content black. This is not needed. <code 
style="color:#000"> can be used instead.

Reproduce code:
---------------
<?php

highlight_string('$foo');

Expected result:
----------------
<code><span style="color: #000000">
$foo</span>
</code>

Actual result:
--------------
&t;code style="color: #000000">
$foo
</code>