Distinct extrusion role for support material interface

xs/src/ExtrusionEntity.hpp

@@ -23,6 +23,7 @@ enum ExtrusionRole {
     erGapFill,
     erSkirt,
     erSupportMaterial,
+    erSupportMaterialInterface,
 };
 
 /* Special flags describing loop */

xs/xsp/ExtrusionPath.xsp

@@ -141,6 +141,7 @@ _constant()
     EXTR_ROLE_GAPFILL                      = erGapFill
     EXTR_ROLE_SKIRT                        = erSkirt
     EXTR_ROLE_SUPPORTMATERIAL              = erSupportMaterial
+    EXTR_ROLE_SUPPORTMATERIAL_INTERFACE    = erSupportMaterialInterface
   PROTOTYPE:
   CODE:
     RETVAL = ix;