use G_OS_WIN32 and G_HAVE_CYGWIN #defines

* app/app_procs.c
* app/gdisplay_color.[ch]
* app/gdisplay_color_ui.c: make the ui usable

* app/gdisplay.c: enable cdisplay support

* modules/Makefile.am
* modules/cdisplay_gamma.c: moved gamma functionality to separate

-Yosh

libgimpbase/gimpdatafiles.c

@@ -34,7 +34,7 @@
 #include <dirent.h>
 #endif
 
-#ifdef NATIVE_WIN32
+#ifdef G_OS_WIN32
 #ifndef S_ISDIR
 #define S_ISDIR(m) (((m) & _S_IFMT) == _S_IFDIR)
 #define S_ISREG(m) (((m) & _S_IFMT) == _S_IFREG)