Add tests to check if apply_config invaldiates existing steps for perimeter count and infill.
Add tests to check if apply_config invaldiates existing steps for perimeter count and infill.

lordofhyphens/Slic3r,alexrj/Slic3r,lordofhyphens/Slic3r,lordofhyphens/Slic3r,lordofhyphens/Slic3r,curieos/Slic3r,alexrj/Slic3r,alexrj/Slic3r,curieos/Slic3r,lordofhyphens/Slic3r,alexrj/Slic3r,alexrj/Slic3r,pieis2pi/Slic3r,pieis2pi/Slic3r,alexrj/Slic3r,curieos/Slic3r,pieis2pi/Slic3r,pieis2pi/Slic3r,curieos/Slic3r,curieos/Slic3r,lordofhyphens/Slic3r,pieis2pi/Slic3r,pieis2pi/Slic3r,curieos/Slic3r