add option to quell dune(-istl) warnings
Comment or add (void) usage of unused arguments.
Avoid signed/unsigned mismatch.
Comment out unused function argument.
Avoid signed/unsigned warning.
Add (all-zero) initialisation of new EquilRecord fields.
Merge remote-tracking branch 'akva2/quell_dune_warnings' into suppress-external-warnings
Fix access to keywords, while still silencing warning.

Previous fix was wrong because it called getKeyword() outside the
hasKeyword() check. Current version (like original code) uses the
short-circuiting behaviour of && to ensure this.
Added more warnings to suppression list, sorted list.
Make function in header file inline.
Merge branch 'suppress-warnings' into suppress-external-warnings
Change option name and generated header names.
Merge pull request #571 from atgeirr/suppress-warnings

Suppress warnings
Merge pull request #575 from atgeirr/suppress-external-warnings

Suppress external warnings