本文转载至 http://blog.csdn.net/zaitianaoxiang/article/details/6657887
http://yueding920.blog.163.com/blog/static/35250890201131410318588/
http://www.cocoabuilder.com/archive/cocoa/192727-leopard-fileextensionsfromtype-deprecation-breaks-saving-with-extension.html
http://www.apple.com.cn/developer/iphone/library/documentation/General/Conceptual/DevPedia-CocoaCore/UniformTypeIdentifier.html