A placeholder for an as-yet-unknown Apple device has appeared in the latest internal build of the iOS 4.1 beta, according to a new report. Citing people familiar with the matter, AppleInsider reports that the latest iOS 4.1 build contains code referencing both the fourth-generation iPod touch—labeled iPod4,1—and a second-generation iPad—labeled iProd2,1. Perhaps more interesting, however, is a listing for “unknownHardware,”…