Test for centroid's variant-awareness

git-svn-id: http://svn.boost.org/svn/boost/trunk@86337 b8fc166d-592f-0410-95f2-cb63ce0dd405
Removed check_input stage - merged into resolve_variant.

git-svn-id: http://svn.boost.org/svn/boost/trunk@86338 b8fc166d-592f-0410-95f2-cb63ce0dd405