Storyboard只支持iOS5.0或者以上的版本

Apple的文档表明storyboard只支持iOS5.0或者以上的版本，网上有好多关于如何在iOS4.3或者以下的版本上使用storyboard的提问，反正看了这个文档可以死心了。

Do you want your app to use storyboards? Storyboards simplify the design process by showing both the views and view controllers of your user interface and the transitions between them. Storyboards are supported in iOS 5 and later and are enabled by default for new projects. If your app must run on earlier versions of iOS, though, you cannot use storyboards and should continue to usenib files.

文档出自https://developer.apple.com/library/ios/#documentation/iphone/conceptual/iphoneosprogrammingguide/AppDesignBasics/AppDesignBasics.html