[adaptivity] Make work for power/composite GridfunctionSpaces.
This fixes a problem of Liesel Schumacher, and should be related to a problem by Timothy Dodwell, see
https://lists.dune-project.org/pipermail/dune-pdelab/2016-January/001096.html.
This fixes a problem of Liesel Schumacher, and should be related to a problem by Timothy Dodwell, see
https://lists.dune-project.org/pipermail/dune-pdelab/2016-January/001096.html.