Fixes unfinished code in timed_wait for systems without POSIX timeout support, such as Darwin

git-svn-id: http://svn.boost.org/svn/boost/trunk@86529 b8fc166d-592f-0410-95f2-cb63ce0dd405
Fix for function declarations which have macroized exception specifications.
Fixes #8812.

git-svn-id: http://svn.boost.org/svn/boost/trunk@86530 b8fc166d-592f-0410-95f2-cb63ce0dd405
Made envelope variant-aware.

git-svn-id: http://svn.boost.org/svn/boost/trunk@86531 b8fc166d-592f-0410-95f2-cb63ce0dd405