Description:
------------
XSLTProcessor::setParameter() seems to be validating if its arguments are valid in XSLT context, but not always. What I'm even more curious about is that these warnings never get into the LibXML's error buffer. That is, libxml_get_errors() returns an empty array when such warnings are to be displayed (regardless of the libxml_use_internal_errors() value).

To make description of the bug simpler, I'm only altering the $params array in the sample code below (which I used to isolate the bug(s?)).

Another (minor) part of this issue is that the namespace is never validated to be an URI (I can live without that one though), regardless of whether two or three arguments are used.

Reproduce code:
---------------
<?php
ini_set('display_errors', 'On');
$params = array();
libxml_use_internal_errors(true);
$proc = new XSLTProcessor;
$proc->importStylesheet(@DOMDocument::loadXML('<?xml version="1.0"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
	<xsl:param name="test1" />
	<xsl:param name="test2" />
	<xsl:template match="/">
		test1: <xsl:value-of select="$test1"/><br />
		test2: <xsl:value-of select="$test2"/><br />
	</xsl:template>
</xsl:stylesheet>'));
$proc->setParameter(null, $params);
echo $proc->transformToXML(DOMDocument::loadXML('<a/>'));
print_r(libxml_get_errors());
?>

Expected result:
----------------
$params = array(
'test1'=>'legal value',
'1'=>'invalid parameter name, but a legal value',
'test2'=>'another legal value');

Should create a warning for $params being an invalid parameter array, ideally pointing explicitly to the "1" parameter, and still apply "test2", since it's a valid parameter. The warning should be part of the LibXML error buffer.

$params = array(
'test1'=> new XSLTProcessor,
'test2'=>'legal value');

Should generate a warning in LibXML's error buffer because of the XSLTProcessor object. This error belongs there, as "normal" arrays can have objects as their values. The same is applicable for any other object, though I'm not sure if __toString() has any influence on the outcome with setParameter(). I believe it should be tried before a warning is reported, and if it's not available, "test1" should not be populated at all (or should I say its last successfully applied value should be used during the transformation).

The same should apply if setParameter() was used with three arguments instead of two, like
$proc->setParameter(null, 'test1', 'legal value');
$proc->setParameter(null, '1', 'invalid parameter name, but a legal value');
$proc->setParameter(null, 'test2', 'another legal value');
and
$proc->setParameter(null, 'test1', new XSLTProcessor);
$proc->setParameter(null, 'test2', 'legal value');
respectively.

Actual result:
--------------
$params = array(
'test1'=>'legal value',
'1'=>'invalid parameter name, but a legal value',
'test2'=>'another legal value');

Shows a warning about $params not being a valid parameter array and doesn't apply any parameter in the array appearing after the first invalid parameter (in the case above: "test2"). No entry in LibXML's error buffer is generated.

$params = array(
'test1'=> new XSLTProcessor,
'test2'=>'legal value');

Throws a catchable fatal error appearing on screen, and executes the transformation, giving "test1" a value of the string "Object", and giving "test2" its expected "legal value".

When using three arguments instead of two, no warnings ever occur anywhere for the first case, and
$proc->setParameter(null, 'test1', new XSLTProcessor);
shows "Wrong parameter count" warning, instead of trying to turn the object into string, and using
$proc->setParameter(null, 'test1',(string) new XSLTProcessor);
shows the same error as when using an array, only it doesn't populate "test1" with the value "Object".

(I haven't tried it, but I'm guessing resources may have similar issues)