add a test to ensure projection_traits is working

.gitattributes

@@ -1427,6 +1427,7 @@ Convex_decomposition_3/test/Convex_decomposition_3/star.nef3 -text
 Convex_hull_2/demo/Convex_hull_2/help/index.html svneol=native#text/html
 Convex_hull_2/doc_tex/Convex_hull_2/convex_hull.png -text
 Convex_hull_2/doc_tex/Convex_hull_2/saarhull.png -text svneol=unset#image/png
+Convex_hull_2/test/Convex_hull_2/ch2_projection_3.cpp -text
 Convex_hull_3/benchmark/Convex_hull_3/compare_different_approach.cpp -text
 Convex_hull_3/benchmark/Convex_hull_3/is_on_positive_side.cpp -text
 Convex_hull_3/demo/Convex_hull_3/CMakeLists.txt -text

Convex_hull_2/test/Convex_hull_2/ch2_projection_3.cpp

@@ -0,0 +1,25 @@
+#include <CGAL/Exact_predicates_inexact_constructions_kernel.h>
+#include <CGAL/convex_hull_2.h>
+#include <CGAL/Projection_traits_xy_3.h>
+#include <iostream>
+#include <fstream>
+
+typedef CGAL::Exact_predicates_inexact_constructions_kernel Kernel;
+typedef CGAL::Projection_traits_xy_3<Kernel> Traits;
+typedef Traits::Point_2 Point_2;
+
+int main(){
+  std::vector<Point_2> points;
+  std::ifstream input("data/CD500");
+  
+  double x,y;
+  while (input >> x >> y){
+    points.push_back(Point_2(x,y,3.));
+  }
+  
+  std::vector<Point_2> ch2;
+  
+  CGAL::convex_hull_2(points.begin(),points.end(),std::back_inserter(ch2),Traits());
+  
+  std::cout << ch2.size() << std::endl;
+}