KML support for Internet Explorer

This PR adds support for KML in Internet Explorer.

IE9's XML support is irritatingly different to the rest of the world. Most of the differences are now abstracted away in `ol.xml`.

Tested in IE9 on Windows 7 and IE10 on Windows 8.  Both render correctly. All versions of IE are horribly slow at parsing large XML files, and IE9 is particularly slow at rendering.

![ol3-kml-ie9](https://f.cloud.github.com/assets/6942/2078233/67a46916-8dbb-11e3-8efd-2a87aecc3ac7.png)