added tests to check for height reset and that one object is printed before another.
added tests to check for height reset and that one object is printed before another.

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