Description:
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The spl_autoload_register function was recently modified (I don't think 
it's documented, though) to allow the pre-pending of functions to the 
stack (see bug #42823).

I'm using pre-pending and am later trying to remove a registered 
function from the end of the stack. This removes ALL methods, not just 
the method I'd intended.

Reproduce code:
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function autoload1() {}

function autoload2() {}

spl_autoload_register('autoload2');

// register autoload1 at the bottom of the stack
spl_autoload_register('autoload1', true, true);

// Output: Array ( [0] => autoload1 [1] => autoload2 )
print_r(spl_autoload_functions());

// unregister autoload2 - autoload1 _should_ be left behind
spl_autoload_unregister('autoload2');

Expected result:
----------------
When running spl_autoload_functions(), I'd expect a single entry to be 
left: array([0] => 'autoload1');

Actual result:
--------------
The array is empty: array();