add option to quell dune(-istl) warnings
Merge remote-tracking branch 'akva2/quell_dune_warnings' into suppress-external-warnings
Added more warnings to suppression list, sorted list.
Merge branch 'suppress-warnings' into suppress-external-warnings
Change option name and generated header names.
Merge pull request #575 from atgeirr/suppress-external-warnings

Suppress external warnings