Update code that uses string buffers (refs #8267).
Treat cast to pointer as compile time error (refs #8334).
Update documentation

git-svn-id: http://svn.boost.org/svn/boost/trunk@83601 b8fc166d-592f-0410-95f2-cb63ce0dd405
Fix most validity errors.

git-svn-id: http://svn.boost.org/svn/boost/trunk@83602 b8fc166d-592f-0410-95f2-cb63ce0dd405
Add test case for multiple variants.

git-svn-id: http://svn.boost.org/svn/boost/trunk@83603 b8fc166d-592f-0410-95f2-cb63ce0dd405