Object doesn't support property or method 'selectSingleNode' in CRM 2013

I've got a webresource called FetchUtil.js, which I think is from the 2011 SDK. I can't find it in my 2013 SDK. There's a funciton in it causing an error:

Object doesn't support property or method 'selectSingleNode'. Here's the code below:

var sFetchResult = xmlhttp.responseXML.selectSingleNode('//a:Entities').xml;

As this is a standard library, I'm reluctant to change it. Is there a 2013 version of this file, or of this method?

Thanks.