Description:
------------
People use defined() to check if a constant is defined so they can later use constant() without any warning or error.

I found these bugs:
1. defined() doesn't forward exceptions
2. defined() try to load class from an invalid constant name (false:::::)
3. produce invalid error line white raising an error if autoloader thrown an exception.

There should be a $autoload param like in class_exists() and interface_exists().


Reproduce code:
---------------
<?
function autoloader($class) {
	throw new Exception(); // line 3
}

spl_autoload_register('autoloader');

function foo() {
	defined('false:::::::'); // line 9
	$a = 10;
	$b = 11;
} // line 12

foo(); // line 14
?>

Expected result:
----------------
From PHP 5.1.2:

Fatal error: Uncaught exception 'Exception' in /root/x.php:3
Stack trace:
#0 [internal function]: autoloader('false')
#1 [internal function]: spl_autoload_call('false')
#2 /root/x.php(9): defined('false:::::::')
#3 /root/x.php(14): foo()
#4 {main}
  thrown in /root/x.php on line 3


Actual result:
--------------
From PHP 5.2.6:

Fatal error: Class 'false' not found in /root/workspace.appserv/XAS/bugTest.php on line 12