atrf-path: added basic graphical output

- gui.h, gui.c: plot sweep results with SDL_gfx
- Makefile: added target-specific variables for SDL and SDL_gfx
- atrf-path.c (main): invoke the GUI if the number of sweeps is zero

tools/atrf-path/gui.h

@@ -0,0 +1,27 @@
+/*
+ * atrf-path/gui.h - Graphical output for atrf-path
+ *
+ * Written 2011 by Werner Almesberger
+ * Copyright 2011 Werner Almesberger
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ */
+
+#ifndef GUI_H
+#define GUI_H
+
+#include <stdlib.h>
+
+#include "sweep.h"
+
+
+#ifdef HAVE_GFX
+void gui(const struct sweep *sweep);
+#else
+#define gui(sweep) abort()
+#endif
+
+#endif /* !GUI_H */