Make releases/2.6 work with dune-functions-2.6
requested to merge carsten.graeser/dune-pdelab:feature/2.6-update-functions-interface into releases/2.6
Cherry-pick two patches from master:
- Fix a missing header by using
LagrangeBasis
instead ofPQkNodalBasis
- Avoid warning by drop using
basis.localIndexSet()