Performance improvements and a small fix.

lib/Doctrine/Connection.php

@@ -668,7 +668,7 @@ abstract class Doctrine_Connection extends Doctrine_Configurable implements Coun
         }
         $class = $name . 'Table';
 
-        if (class_exists($class) && in_array('Doctrine_Table', class_parents($class))) {
+        if (class_exists($class, false) && in_array('Doctrine_Table', class_parents($class))) {
             $table = new $class($name, $this);
         } else {
             $table = new Doctrine_Table($name, $this);