different versin of Constrained_triangulation_plus_2.h
are now provided for :
exact computations
exact predicates and approximate intersection construction
no support of constraint intersections
into distinct function to avoid duplication of code
Adapt Constrained_triangulation_2 and Constrained_Delaunay_triangulation
to the design of
Constrained_triangulation_plus_2
where the template parameter can either Constrained_triangulation_2
or Constrained_Delaunay_triangulation