Fix for issue #336 (incorrect ndofs for interior face loop)

Fix proposed by Lawrence: multiply number of dofs by two for interior facets.
add CircleManifoldMesh (gdim 2, tdim 1)
add non-extruded circumference tests
add radial-extrusion-of-circle test
add poisson test
Merge pull request #337 from firedrakeproject/fix_ndof_inparloop_over_interior_facets

* fix_ndof_inparloop_over_interior_facets:
  Fix for issue #336 (incorrect ndofs for interior face loop)
Merge pull request #331 from firedrakeproject/circle_surface_mesh

* circle_surface_mesh:
  add poisson test
  add radial-extrusion-of-circle test
  add non-extruded circumference tests
  add CircleManifoldMesh (gdim 2, tdim 1)
Pass mesh generator options for 2D meshes

This means we actually produce regular meshes (rather than just a
delauney triangulation with starting from specified seed points).