Description:
------------
I've a function __autoload in my script. I want to use class_exists to determine if a class definition has been included but i don't want to load it.

However, class_exists call __autoload systematically when a class definition hasn't been loaded.

This problem poses problems of compatibility with previous versions.  Indeed, many scripts used this function before using a include.

Reproduce code:
---------------
function __autoload($classname) {
  echo 'i want to load ['.$classname.']<br>';
}

class A {}

if (class_exists('B') == false) 
  echo "Class B don't exist !<br>";
else
  echo "Class B exist !<br>";

if (class_exists('A') == false) 
  echo "Class A don't exist !<br>";
else
  echo "Class A exist !<br>";


Expected result:
----------------
Class B don't exist !
Class A exist !


Actual result:
--------------
i want to load [B]
Class B don't exist !
Class A exist !