Boost.Log merged to release.

git-svn-id: http://svn.boost.org/svn/boost/branches/release@84333 b8fc166d-592f-0410-95f2-cb63ce0dd405
Updated changelog, corrected comments.

git-svn-id: http://svn.boost.org/svn/boost/branches/release@84336 b8fc166d-592f-0410-95f2-cb63ce0dd405