Test for the getArrayCopy method in AbstractRestultSet

If you're using the `ArraySerializable` hydrator, then you will have a
method called `getArrayCopy` in your row object, so allow
`AbstractResultSet` to use it.

library/Zend/Db/ResultSet/AbstractResultSet.php

@@ -268,7 +268,7 @@ public function toArray()
                 $return[] = $row;
             } elseif (method_exists($row, 'toArray')) {
                 $return[] = $row->toArray();
-            } elseif ($row instanceof ArrayObject) {
+            } elseif (method_exists($row, 'getArrayCopy')) {
                 $return[] = $row->getArrayCopy();
             } else {
                 throw new Exception\RuntimeException(