When using different class loaders

ClassLoader::classExists($class); will fail if different class loader is used which does not return any boolean value. This includes Symfony2 UniversalClassLoader

I have never used this function before because native PHP method class_exits($class, true) first will try to autoload. But if the class does not exist
and you are using Doctrine\Common::ClassLoader and you call class_exists($class) it will trigger fatal error. This behavior makes it impossible to make code compatible
with different class loading mechanisms for Doctrine2