Adopted use of FL_LIBRARY #define symbol under Mac OS X. This allows to compile

client applications without including Mac OS system headers, with a gain in speed of 
compilation and portability. The source files of all FLTK libraries must now be compiled with 
-DFL_LIBRARY under Mac OS X. Make, CMake and Xcode project support files
have been modified accordingly.

git-svn-id: file:///fltk/svn/fltk/branches/branch-1.3@8113 ea41ed52-d2ee-0310-a9c1-e6b18d33e121

test/demo.cxx

@@ -136,6 +136,8 @@ const char *default_menu[] = {
 #    define chdir _chdir
 #    define putenv _putenv
 #  endif // !__WATCOMC__
+#elif defined USING_XCODE
+#include <Carbon/Carbon.h>
 #else
 #  include <unistd.h>
 #endif