Henry “Hap” Plain, a collector of rare Mac prototypes, revealed an unreleased prototype Apple Mac mini with a built-in iPod dock in an interview with Cult of Mac. According to Plain, a friend suggested that Apple originally planned on releasing the Mac mini at the same time as the new iPod that would dock on its top, but the iPod project was running behind schedule, so Apple left the feature out. While Plain says that the iPod in question…