Removed dependency on Math::Clipper

xs/xsp/Clipper.xsp

@@ -10,6 +10,16 @@
 
 %{
 
+IV
+_constant()
+  ALIAS:
+    JT_MITER        = jtMiter
+    JT_ROUND        = jtRound
+    JT_SQUARE       = jtSquare
+  CODE:
+    RETVAL = ix;
+  OUTPUT: RETVAL
+
 Polygons
 offset(polygons, delta, scale = CLIPPER_OFFSET_SCALE, joinType = ClipperLib::jtMiter, miterLimit = 3)
     Polygons                polygons

xs/xsp/Polygon.xsp

@@ -25,6 +25,7 @@
         %code{% const char* CLASS = "Slic3r::Polyline"; RETVAL = THIS->split_at_first_point(); %};
     double area();
     bool is_counter_clockwise();
+    bool is_clockwise();
     bool make_counter_clockwise();
     bool make_clockwise();
     bool is_valid();