CircularKernel::Split_2

A model fo of this type must provide:

void	fo ( CircularKernel::Circular_arc_2 a, CircularKernel::Circular_arc_point_2 p, CircularKernel::Circular_arc_2 &a1, CircularKernel::Circular_arc_2 &a2)
		Splits arc $$a at point $$p, which creates arcs $$a1 and $$a2. Precondition: $$a is $$x-monotone, and $$p lies on $$a.
void	fo ( CircularKernel::Line_arc_2 l, CircularKernel::Circular_arc_point_2 p, CircularKernel::Line_arc_2 &l1, CircularKernel::Line_arc_2 &l2)
		Same for a line arc.