Description:
------------
spl_autoload_unregister can't handle spl_autoload_functions results when autoloader is static method and register as string with \ prefix

real example:
https://github.com/goaop/framework/blob/master/src/Instrument/ClassLoading/AopComposerLoader.php#L106
buggy when load under Bitrix: https://github.com/matiaspub/bxApiDocs/blob/master/modules/main/lib/loader.php#L462

Test script:
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class Auto { public static function loader() {}}
$autoloader = '\Auto::loader';

echo (int)spl_autoload_register($autoloader);
foreach (spl_autoload_functions() as $loader) {
    echo (int)spl_autoload_unregister($loader);
}
echo (int)count(spl_autoload_functions());

Expected result:
----------------
110

Actual result:
--------------
101