Mac OS X: replace some deprecated APIs with modern equivalents (thank…

…s, Alex!).

Fixes Bugzilla #2858.

src/video/cocoa/SDL_cocoaevents.h

@@ -25,6 +25,7 @@
 
 extern void Cocoa_RegisterApp(void);
 extern void Cocoa_PumpEvents(_THIS);
+extern void Cocoa_SuspendScreenSaver(_THIS);
 
 #endif /* _SDL_cocoaevents_h */