[Dune] Installation of dune pdelab

[Christian Engwer]

Hi Peter,

> what I apparently was missing was a opts file to that defines
> "dune_symlink_to_source_files". This fixed the
> 
> > CMake Error at CMakeLists.txt:3 (dune_symlink_to_source_files):
> >    Unknown CMake command "dune_symlink_to_source_files".

do I get your right and there are some files not properly installed?

Christian