[PATCH] in_class_exists() for detecting __autoload() called by class_exists() and interface_exists()

Hi again,

The attached patches for PHP 5.3 and PHP 6 add in_class_exists(). The
function is intended to be used in __autoload(). The following test
script demonstrates its usage:

<?php
var_dump(in_class_exists('test'));
function __autoload($class)
{
var_dump(in_class_exists($class));
eval ('class ' . $class . ' {}');
}

$a = new Bungalow; // autoload called, not because of class_exists(),
bool(false)
class_exists('test'); // autoload called because of class_exists(),
bool(true)
class_exists('test'); // class exists, no autoload, no output
$a = new test; // autoload not called, no output
$a = new Another; // autoload called, not because of class_exists(),
bool(false)
?>

outputting:

bool(false)
bool(false)
bool(true)
bool(false)

The purpose is to allow an autoload handler to detect whether it is safe
to use die() or some other method of terminating execution. A user
calling class_exists() clearly expects a return from autoload, whereas a
user instantiating an object will expect a fatal error if the class
cannot be found.

This is useful for PEAR2 as a means of displaying helpful information on
locating missing class files only in cases where a fatal error would
result anyways.

Thanks,
Greg