Description:
------------
When I change the driver from DB to MDB, I get the following message as detailed below.

DB_NestedSet  v.1.2.4
MDB           v.1.1.3



Reproduce code:
---------------
		$treeNodes = $this->nestedSet->getAllNodes(true, true, array(
																	'cols' => 'table.url, table.url_text'
																));

		// render output
		$options = array(
		    'structure' => $treeNodes,
		    'textField' => 'url_text',
		    'linkField' => 'url',
			'options' => array('icon' => 'folder.gif',
								'expandedIcon' => 'folder-expanded.gif')
		);


		$this->output =& DB_NestedSet_Output::factory($options, 'TreeMenu');

Expected result:
----------------
A DHTML tree Menu (works fine using DB rather than MDB)

Actual result:
--------------
Fatal error: Call to undefined function: quote() in E:\.....\libs\pear\DB\NestedSet.php on line 613