added hasImpl()

lib/Doctrine/Configurable.php

@@ -226,6 +226,18 @@ abstract class Doctrine_Configurable extends Doctrine_Locator_Injectable
         return $this->_impl[$template];
     }
     
+    
+    public function hasImpl($template)
+    {
+        if ( ! isset($this->_impl[$template])) {
+            if (isset($this->parent)) {
+                return $this->parent->hasImpl($template);
+            }
+            return false;
+        }
+        return true;
+    }
+
     /**
      * getCacheDriver
      *