Ported Print::bounding_box(), Print::total_bounding_box(), Print::skirt_flow(), Print:skirt_first_layer_height() to XS

lib/Slic3r/Print/SupportMaterial.pm

@@ -17,9 +17,6 @@ has 'interface_flow'    => (is => 'rw', required => 1);
 
 use constant DEBUG_CONTACT_ONLY => 0;
 
-# how much we extend support around the actual contact area
-use constant MARGIN => 1.5;
-    
 # increment used to reach MARGIN in steps to avoid trespassing thin objects
 use constant MARGIN_STEP => MARGIN/3;