Removal of dune-common/dune/function.hh makes TNNMG unusable
the deprecated file with the interfaces
Dune::VirtualFunction is now deleted.
dune-tnnmg still depends on this file in the definition of the functional classes.
I am opening an issue since I am not sure how severe the problem is.
A workaround would be to transfer the old interface from the
dune-common module to
dune-tnnmg, since we only need a few members and methods.