Microsoft is yet to fully announce which features will make it into the Windows Phone 7.8 upgrade, but a leaked document may have just shed some light on this.Windows Phone 8 will be launched in October, but current handsets running Windows Phone 7 won't be eligible for the upgrade, instead having to settle for the less feature-packed 7.8 update.We've already learned that Windows Phone 7.8 will sport the new homescreen tiles, with variable sizes allowing more to fit on the display, and now a document which has shown up on SmartPhone France reveals greater detail.