References to a third-generation Apple TV have been spotted in the GM version of iOS 5. 9to5Mac reports that deep inside the iOS file system lies a reference to an Apple TV 3,1, which would be expected to represent a substantial upgrade from the current 2,1 model. The report goes on to suggest that such a model could feature an A5 processor to allow for 1080p video output support, and thus merit the addition of 1080p content to the iTunes Store. It…