Ported Slic3r::GCode::needs_retraction() to XS

xs/xsp/GCode.xsp

@@ -152,6 +152,8 @@
     void set_origin(Pointf* pointf)
         %code{% THIS->set_origin(*pointf); %};
     std::string preamble();
+    bool needs_retraction(Polyline* travel, ExtrusionRole role)
+        %code{% RETVAL = THIS->needs_retraction(*travel, role); %};
     std::string retract(bool toolchange = false);
     std::string unretract();
     Clone<Pointf> point_to_gcode(Point* point)