feature-detect for Document Fragments

reports true as expected in IE 6-10, Chrome, Opera, probably in Firefox
reports false on a few old Nokia handsets in the office, probably on old Blackberries too

As using Document Fragments is considered a performance and stability best-practice for DOM manipulation, I think it's worth knowing when you can actually use this technique safely.

I have probably been a little too pedantic, so do let me know if some of the tests ought to be trimmed.