[backport/2.6] [!370] Catch polymorphic exceptions by reference
Merge branch 'catch-polymorphic-exception-by-reference' into 'master'
g++-8 warns about this, e.g.,
/home/sander/dune-book/code/dune-pdelab/dune/pdelab/newton/newton.hh:672:14: warning: catching polymorphic type ‘class Dune::PDELab::NewtonDefectError’ by value [-Wcatch-value=]
catch (NewtonDefectError)
^~~~~
See merge request pdelab/dune-pdelab!370
(cherry picked from commit 51238823)
a4fba9a3 Catch polymorphic exceptions by reference