[release] fixes a few unused parameter warnings

This is part of the patch provided by Rene in Flyspray 1355.
(cherry picked from commit 99d2488527ecbebe97fb8b1554acccdb6a348a2f)

Signed-off-by: Markus Blatt <markus@dr-blatt.de>
[release] Fixes unused parameter warnings.

This the customized rest of Rene's patch. To make doxygen happy
we use DUNE_UNUSED_PARAMETER.
(cherry picked from commit 48730f4a87a27af2077ffa3e6114e03393e6603a)

Signed-off-by: Markus Blatt <markus@dr-blatt.de>
[release] Removes the rest of the unused parameter warnings
(cherry picked from commit d709d8d82004b03eb78ad3e6f3a7abb15d4770c0)

Signed-off-by: Markus Blatt <markus@dr-blatt.de>
[bugfix,documentation] Spelling
(cherry picked from commit 592c2d3989bc7893b605232c18e08cd83af52fc6)

Signed-off-by: Markus Blatt <markus@dr-blatt.de>