Use size_t instead of int for number of points

This squashes warnings under Visual Studio 12

contrib/poly2tri/poly2tri/sweep/sweep_context.cc

@@ -96,8 +96,8 @@ void SweepContext::InitTriangulation()
 
 void SweepContext::InitEdges(std::vector<Point*> polyline)
 {
-  int num_points = polyline.size();
-  for (int i = 0; i < num_points - 1; i++) {
+  std::size_t num_points = polyline.size();
+  for (std::size_t i = 0; i < num_points - 1; i++) {
     edge_list.push_back(new Edge(*polyline[i], *polyline[i + 1]));
   }
   edge_list.push_back(new Edge(*polyline.back(), *polyline.front()));

contrib/poly2tri/poly2tri/sweep/sweep_context.h

@@ -64,7 +64,7 @@ void set_tail(Point* p1);
 
 Point* tail();
 
-int point_count();
+std::size_t point_count();
 
 Node& LocateNode(Point& point);
 
@@ -156,7 +156,7 @@ inline AdvancingFront* SweepContext::front()
   return front_;
 }
 
-inline int SweepContext::point_count()
+inline std::size_t SweepContext::point_count()
 {
   return points_.size();
 }