Tips & Tricks for conditional iOS3, iOS3.2 and iOS4 code

Please note: this article is part of the older "Objective-C era" on Cocoa with Love. I don't keep these articles up-to-date; please be wary of broken code or potentially out-of-date information. Read "A new era for Cocoa with Love" for more. In this post, I'll show you ways to determine which version of iOS you are running on and show you how to write a macro that can both conditionally compile an