Eliminate causes for AppleClang warnings

[SeanCurtis-TRI]

This cleans up a few inconsequential items that would otherwise trigger warnings (and errors if so promoted) in AppleClang.

• Unused parmeters
• Implicit deletion of copy assignment (by introduction of an unnecessary explicit copy constructor).

[ahornung]

This PR has a strange history and conflicts. Could you rebase the actual fixes onto the newest devel branch? There are some CI run that should work as well.

[SeanCurtis-TRI]

Yeah. Sorry about that. I'd written it against v1.10.0 and failed to rebase it against devel. I've now rebased it so things should be much cleaner.

Note: the original PR included a change in Vector::operator< that was missing in v1.10.0 but was in place in devel. So, a v1.10.1 would definitely benefit from the current state of devel even if this PR is rejected.

[ahornung]

Thanks! With all the recent changes and rewrite of the CMake usage, the next release will probably be a "breaking" v2.0.0. Do you explicitly need these changes (+ other fixes) backported to a 1.10 bugfix release?

[SeanCurtis-TRI]

I currently have mac CI build disabled (partly) due to things like this. A v1.10 bug fix would certainly help with that. (A smaller effort to resolve than may potentially be wrapped up in a major version change.) However, re-enabling that CI is currently a low priority for me. If there's enough interest in the community, I'd happily put it to use, but don't feel like you have to do it strictly for my needs.