Merge branch 'johanhake/multistage'
Merge branch 'mliertzer/convert_2d_disspack_mesh'
Updates for KSPSetOperators change in PETSc-dev.

DOLFIN compiles against PETSc-dev, but logic around preconditioner use needs updating.
PETScSNESSolver updates for change in PETSc interface.
Merge branch 'garth/update-petsc-ksp-interface' into next