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

app/dialogs/module-dialog.c

@@ -453,7 +453,7 @@ valid_module_name (const char *filename)
 
   len = strlen (basename);
 
-#if !defined(WIN32) && !defined(__EMX__)
+#if !defined(G_OS_WIN32) && !defined(G_HAVE_CYGWIN) && !defined(__EMX__)
   if (len < 3 + 1 + 3)
     return FALSE;