FIX: Gallery

Updates to the gallery. I can't run all of the examples currently (!), so I can't include all of them.
@lcampagn made some changes here to avoid warnings. These are because `X == None` is going to become element-wise, so better to compare to `-1` here (which should give the same result). The one above is necessary because the `self.intersect_edge_arrays` can give invalid values -- they're caught in that function, but not (in master) in the lines above.