Added 2 utility metafunctions for variants. Necessary to make some algos variant aware.

git-svn-id: http://svn.boost.org/svn/boost/trunk@86584 b8fc166d-592f-0410-95f2-cb63ce0dd405
Tests for variant aware envelope.

git-svn-id: http://svn.boost.org/svn/boost/trunk@86585 b8fc166d-592f-0410-95f2-cb63ce0dd405
Thread: Added caller_context.hpp; Change executor by Executor template parameter in async; update the number of time the failing tests are run to catch all the compilers.

git-svn-id: http://svn.boost.org/svn/boost/trunk@86586 b8fc166d-592f-0410-95f2-cb63ce0dd405
Chrono: use * instead of / when testing floats.

git-svn-id: http://svn.boost.org/svn/boost/trunk@86587 b8fc166d-592f-0410-95f2-cb63ce0dd405
fix up of issues created removal of support for older compilers

git-svn-id: http://svn.boost.org/svn/boost/trunk@86588 b8fc166d-592f-0410-95f2-cb63ce0dd405
fix up of issues created by removal of support for older compilers

git-svn-id: http://svn.boost.org/svn/boost/trunk@86589 b8fc166d-592f-0410-95f2-cb63ce0dd405