Merged latest changes from trunk.

git-svn-id: http://svn.boost.org/svn/boost/branches/release@86164 b8fc166d-592f-0410-95f2-cb63ce0dd405
Temporarily reverted the last commit [86164], until 1.55 beta ships.

git-svn-id: http://svn.boost.org/svn/boost/branches/release@86166 b8fc166d-592f-0410-95f2-cb63ce0dd405