To be honest I don't remember exactly what dependencies on iOS 7 we have; there are so many API additions in each OS. In part it's simply because we no longer test on iOS 6 and we don't want to declare compatibility with an untested OS.
You could try changing the target OS version back to iOS 6 and building, to see if there are any errors, but that won't catch all dependencies; you'd need to actually try running on iOS 6 and look for runtime exceptions. (I really wish Xcode had a way to enforce that code is only using available APIs, but it doesn't.)
—Jens