Merge from trunk:
* Fix issue with const rvalue references in Boost.Variant (fixes #8988)
* Get rid of Boost.Variant hand written non-usable move emulation and use Boost.Move instead(refs #7601). This does not mean that Boost.Variant supports move emulation now, but removes duplicate/non-working code and makes sure that Boost.Variant is able to work with boost::move