[bug 931274] Detect Windows 8.1 in AAQ & KB

this adds the Windows 8.1 useragent to browserdetect.js & aaq.js 
and unrecognised WinNT useragents should fall-back to a plain "Windows" label in the AAQ

this is a first timer, so please don't be too harsh on me if i've missed something obvious or done something wrong ;-)

r?