Add a warning if the native fileselector isn't available.

git-svn-id: svn://pulkomandy.tk/GrafX2/trunk@1807 416bcca6-2ee7-4201-b75f-2eb2f807beb1

src/filesel.c

@@ -120,7 +120,8 @@ byte Native_filesel(byte load)
     // Check if cancel
     return CommDlgExtendedError();
   }
-#else
+#else ifndef(__linux__) // This makes no sense on X11-oriented platform. Nothing is really native there.
+  #warning "EXPERIMENTAL function for native fileselector not available for this platform!"
   return 255; // fail !
 #endif
 }