Description:
------------
When trying to load a string containing an HTML-encoded 
non-breaking space (" ") with 
simplexml_load_string, I get the following warning:

Warning:  Entity: line 14: error: Entity 'nbsp' not 
defined in /Library/WebServer/Documents/simple.php on 
line 11
 
But other HTML-escaped characters like > and < 
make it through fine.

Reproduce code:
---------------
<?php
$xmlstr = <<<XML
<?xml version='1.0'?>
<rss>
<channel>
<item>
 <title>This is the title</title>
 <link>http://globelogger.com</link>
 <description>This&nbsp;is the description</description>
</item>
</channel>
</rss>
XML;

$xml = simplexml_load_string(utf8_encode($xmlstr)); 
foreach($xml->channel->item as $item) { 
echo "<b><a href=".$item->link.">".$item->title."</a></b><br>".$item->description."<p>";
}
?>

Expected result:
----------------
<b><a href=http://globelogger.com>This is the title</
a></b><br>This is the description<p>

Actual result:
--------------
Warning:  Entity: line 7: error: Entity 'nbsp' not 
defined in /Library/WebServer/Documents/test.php on 
line 15
 
 Warning:   This?is the description in /Library/
WebServer/Documents/test.php on line 15
 
 Warning:                          ^ in /Library/
WebServer/Documents/test.php on line 15
 
 Warning:  Invalid argument supplied for foreach() in /
Library/WebServer/Documents/test.php on line 16