Fix up createSection calls in line with petsc4py changes

Number of fields is now determined directly from the length of the
numComp argument, rather than passed in separately.
Try old createSection calling convention first
Merge pull request #343 from firedrakeproject/petsc4py-compat

* petsc4py-compat:
  Try old createSection calling convention first
  Fix up createSection calls in line with petsc4py changes
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).
tweak test tolerance for new mesh