Enhance International Input Support for Mac OS X

by Jiang Jiang for Simple DirectMedia Layer

Design and implement international text input support for SDL, mainly focused on Mac OS X. My aim is to: 1. Complete a clean, SDL-style API for international text input, work with other implementors on other platforms, if there is any. 2. Give complete implementation of the above API on Mac OS X 10.5. 3. Make sure the API works well enough with all major input methods (including traditional text services manager based and 10.5 IMKit based input methods)