Description:
------------
When you set a string variable with a value like "return any_class::any_method();" and use it on "is_callable" PHP core function, the autoloading is invoked trying to load a class named "return any_class".

Test script:
---------------
<?php

function __autoload($class) {
    printf("Required class: '%s'\n", $class);
}

$code =	'return foo::bar();';

var_dump(is_callable($code));

Expected result:
----------------
bool(false)

Actual result:
--------------
Required class: 'return foo'
bool(false)