Optimize isSubclassOf checks

- Suggested by @marc-mabe -- if is_subclass_of() returns true, we can return
  immediately. This allows us to skip the version_compare() when it passes.
- Removed Zend\Stdlib\SubClass, as I evidently missed doing so in zendframework/zendframework#1852

src/AutoloaderFactory.php

@@ -208,12 +208,12 @@ protected static function getStandardAutoloader()
      */
     protected static function isSubclassOf($className, $type)
     {
-        if (version_compare(PHP_VERSION, '5.3.7', '>=')) {
-            return is_subclass_of($className, $type);
-        }
         if (is_subclass_of($className, $type)) {
             return true;
         }
+        if (version_compare(PHP_VERSION, '5.3.7', '>=')) {
+            return false;
+        }
         if (!interface_exists($type)) {
             return false;
         }