extrude issues

I was playing around with extrude_2d and found two issues with

#!/usr/bin/env python
# -*- coding: utf-8 -*-
#
import meshio

import dolfin
import mshr

# box for reference
box = mshr.Box(dolfin.Point(-3, -1, -0.1), dolfin.Point(3, 1, 0.1))

# triangle
t1 = mshr.Polygon([
        dolfin.Point(2.5, -0.5, 1),
        dolfin.Point(2.5,  0.5, 1),
        dolfin.Point(1.5, -0.5, 1)
        ])
g3d = mshr.Extrude2D(t1, -2)

m = mshr.generate_mesh(box + g3d, 20, "cgal")

meshio.write(
        'test.e',
        m.coordinates(),
        {'tetra': m.cells()}
        )

The extrusion will always start as z-level 0, independently of the z-values of the Polygon points. Perhaps the extrusion can be designed a little more generally here to allow for specifying a direction of extrusion, perhaps even with a rotation angle. (Not sure what CGAL supports here, the ideas come from Gmsh.)
There are some funny artifacts at the bottom side of the reference Box

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