fixes most of the python2 unit tests

src/Circulator.hh

src/Iterator.hh

tests/test_property.py

tests/test_trimesh_circulator_face_edge.py

tests/test_trimesh_circulator_face_face.py

tests/test_trimesh_circulator_face_halfedge.py

tests/test_trimesh_circulator_face_vertex.py

tests/test_trimesh_circulator_halfedge_loop.py

tests/test_trimesh_circulator_vertex_edge.py

tests/test_trimesh_circulator_vertex_face.py

tests/test_trimesh_circulator_vertex_ihalfedge.py

tests/test_trimesh_circulator_vertex_ohalfedge.py

tests/test_trimesh_circulator_vertex_vertex.py

tests/test_trimesh_collapse.py

tests/test_trimesh_iterators.py