Disable autoloading when doing class_exists()

First I don't know why the above check is needed at all (if `Hybrid_Storage` is already loaded). But the above line is triggering external autoloaders of libraries that include `hybridauth/Auth.php`. Given that `hybridauth` doesn't have it's own autoloader yet, it makes sense to disable autoloading on that check.
Merge pull request #247 from ddinchev/patch-1

Disable autoloading when doing class_exists()