force_mobile_format does not check for XHR requests

[thirtyseven]

When using has_mobile_fu true to force requests to be mobile, XMLHttpRequests are included, which breaks AJAX. While this is in line with the documentation, I found it to be rather unexpected, since this mode is meant to be used during testing, when you likely will also be using AJAX requests.

This behavior should be easy to change and would make mobile_fu more useful.