Fix of

"Multimaterial printer switches filament at the wrong time during a print"
https://github.com/prusa3d/Slic3r/issues/607

There was a single layer between the raft top and the object first layer
missing on the wipe tower, and after this missing layer all the tool
changes were shifted by one layer, meaning two color print had the colors
switched.

xs/src/libslic3r/Layer.hpp

@@ -161,7 +161,9 @@ public:
     // Is there any valid extrusion assigned to this LayerRegion?
     virtual bool has_extrusions() const { return ! support_fills.empty(); }
 
-protected:
+//protected:
+    // The constructor has been made public to be able to insert additional support layers for the skirt or a wipe tower
+    // between the raft and the object first layer.
     SupportLayer(size_t id, PrintObject *object, coordf_t height, coordf_t print_z, coordf_t slice_z) :
         Layer(id, object, height, print_z, slice_z) {}
     virtual ~SupportLayer() {}