(svn r8605) -Codechange: [OSX] changed all objective C to objective C++

This will permanently solve the issue where compilation on OSX broke because C++ code was added to some header files

   -Note: (important if you develop mac specific code)
   taken from http://developer.apple.com/releasenotes/Cocoa/Objective-C++.html           
    gdb lacks an integrated C++ with Objective-C parser. This means that gdb won't be able to evaluate expressions that contain both C++ and Objective-C constructs.
    gdb assumes that the language for ".mm" files is C++.
    you can change it to objective C by typing: (gdb) set language objc 
    Mixing C++ and objective C has some limitation (see link for all of them)

src/os/macosx/macos.h

@@ -11,15 +11,9 @@
  * the function then adds text that tells the user to update and then report the bug if it's present in the newest version
  * It also quits in a nice way since we call it when we know something happened that will crash OpenTTD (like a needed pointer turns out to be NULL or similar)
  */
-#ifdef __cplusplus
-extern "C" {
-#endif //__cplusplus
-	void ShowMacDialog ( const char *title, const char *message, const char *buttonLabel );
-	void ShowMacAssertDialog ( const char *function, const char *file, const int line, const char *expression );
-	void ShowMacErrorDialog(const char *error);
-#ifdef __cplusplus
-}
-#endif //__cplusplus
+void ShowMacDialog ( const char *title, const char *message, const char *buttonLabel );
+void ShowMacAssertDialog ( const char *function, const char *file, const int line, const char *expression );
+void ShowMacErrorDialog(const char *error);
 
 // Since MacOS X users will never see an assert unless they started the game from a terminal
 // we're using a custom assert(e) macro.