* lib/geometry.h:
	* lib/connection.[ch]:
	* lib/poly_conn.[ch]:
	* lib/polyshape.[ch]:
	* lib/bezier_conn.[ch]:
	* lib/beziershape.[ch]:
	* lib/orth_conn.[ch]:
	* lib/neworth_conn.[ch]:
	* lib/element.[ch]: Changed a bit the _update_boundingbox()
	interface. Now the parent elements have an extra_spacing
	structure, which child objects just need to fill, to take care of
	most arrow & line width extra space needs.

	* objects/**/*.c: updated all objects to the new interface.
	While at it, killed all instances of (Object *) downcasts (phew !)

	* objects/GRAFCET/condition.c: removed the arrowhead, which IEC848
	doesn't speak about.