Fix issue 206.
Update for PETSc interface change. PETSc has renamed MatGetVecs -> MatCreateVecs.
Merge branch 'jan/fix-issue-206'
Merge branch 'garth/update-for-petsc-change'
Add error message when assembling point integrals rather than silently
returning zero.
Add back absolute tolerance to PointIntegralSolver
  -- Also add a safe guard to absolute tolerance check. It is only kicking in when the residual
     has not changed between two Newton iterations.
Merge branch 'johanhake/fix-absolutetolerance-pointintegralsolver'
Merged master into chris/parallel-refinement-improvements