Fix xpath issues in internet explorer 11.

The navigator appname changed in IE11 and we need to continue using the activexobject because document.evaluate still isn't available in IE11.


Bigger description:
navigator.appName only returns 'Microsoft Internet Explorer' in IE10 and lower, IE11 returns 'Netscape'. And document.evaluate is still not present in IE11, though the DOMParser is. 

The easiest way to fix is to continue using the ActiveXObject, can check if we need to do that (i.e. if it is IE) by looking for document.evaluate. Also detecting IE should be the same in both xpath.js and xml.js since document.evaluate is what both hinge on. Currently the xml detects IE11 incorrectly and xpath detects it correctly.

Tested in chrome, firefox, IE 7-11 and Opera but this is a low level change so should maybe wait for the travis results before pulling.