iOS backwards compatibility

http://longweekendmobile.com/2011/03/15/the-backwards-compatibility-blues-supporting-ios-3-1-4-2/

http://cocoawithlove.com/2010/07/tips-tricks-for-conditional-ios3-ios32.html

http://stackoverflow.com/questions/3313786/ios-4-app-crashes-at-startup-on-ios-3-1-3-symbol-not-found-nsconcretestackblo