Merge from trunk:
* Update docs of Boost.Variant. Add advice about recursive_wrapper performance (fixes #7718)

git-svn-id: http://svn.boost.org/svn/boost/branches/release@84105 b8fc166d-592f-0410-95f2-cb63ce0dd405
Merge fix for undefined behaviour/typo.

git-svn-id: http://svn.boost.org/svn/boost/branches/release@84111 b8fc166d-592f-0410-95f2-cb63ce0dd405
Spirit: merging from trunk

git-svn-id: http://svn.boost.org/svn/boost/branches/release@84119 b8fc166d-592f-0410-95f2-cb63ce0dd405