When leveling, the center circle is now shown when the pointer approaches it.

- solidify/Makefile: added util.o
- solidify/util.h, solidify/util.c (draw_circle): wrapper for gdk_draw_arc
- solidify/Makefile: added style.o
- solidify/style.h, solidify/style.c, solidify/solidify.c (main): GUI style
  parameters and items
- solidify/level.c (scroll_z. scroll_xy, scroll_event, level),
  solidify/overlap.c (scroll_event, overlap): renamed "da" to "darea", to
  avoid confusion with "da" for GdkDrawable in style.c
- solidify/level.c (r_center, scroll_event): moved center radius
  calculation to separate function
- solidify/level.c (draw_image): renamed to draw_map
- solidify/level.c (draw_image): draw an on-screen display (OSD)
- solidify/level.c (scroll_z, scroll_xy, expose_event, level): propagate
  OSD on/off switch
- solidify/level.c (scroll_event, motion_notify_event, level): enable OSD
  when approaching the center circle

solidify/solidify.c

@@ -18,6 +18,7 @@
 
 #include "face.h"
 #include "solid.h"
+#include "style.h"
 #include "level.h"
 #include "overlap.h"
 
@@ -102,6 +103,8 @@ static void gui(void)
 	level(canvas, solid.a);
 	active = solid.a;
 
+	init_style(root->window);
+
 	gtk_widget_show_all(root);
 
 	g_signal_connect(G_OBJECT(root), "key-press-event",