Description:
------------
XSLT document() call times out when calling a php script that starts a valid session.  Calling the php script directly with a valid session ID works fine.

Happened on Apache 2.0.59 and IIS 6.0 on Windows.  PHP version is 5.1.6.

Reproduce code:
---------------
Note session.name = SID

index.php:
<?php
session_start();

$xmlDoc = 'http://'. $_SERVER['HTTP_HOST'] . '/phpbug/main.xml';
$xslDoc = 'http://'. $_SERVER['HTTP_HOST'] . '/phpbug/main.xsl';

$xml = DomDocument::load($xmlDoc);
$xsl = DomDocument::load($xslDoc);

$xslt = new XSLTProcessor();
$xslt->importStylesheet($xsl);
$xslt->setParameter(null, 'sid', session_id());

$doc = $xslt->transformToDoc($xml);
echo $doc->saveHTML();
?>

main.xml:
<document>
  <foo>Foo</foo>
</document>

main.xsl:
<xsl:stylesheet	version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:output method="html" indent="no"/>
  <xsl:template match="*">
    <xsl:variable name="sessionxml">session.xml.php?SID=<xsl:value-of select="$sid"/></xsl:variable>
    <xsl:value-of select="/document/foo"/>
    <xsl:value-of select="document($sessionxml)/document/bar"/>
  </xsl:template>
</xsl:stylesheet>

session.xml.php:
<?php
session_start();
header('Content-Type: text/xml');
?>
<document>
  <bar>Bar</bar>
</document

Expected result:
----------------
FooBar

(This is the result if session_start() is commented out in session.xml.php)

Actual result:
--------------
PHP call times out, then:

Warning: XSLTProcessor::transformToDoc(http://localhost/phpbug/session.xml.php?SID=5vg8lbefrjnd72vjmhdensrmg2) [function.XSLTProcessor-transformToDoc]: failed to open stream: HTTP request failed!