Fix for evaluation at float precision.

git-svn-id: http://svn.boost.org/svn/boost/trunk@84944 b8fc166d-592f-0410-95f2-cb63ce0dd405
Thread: rollback change in #8070 as this includes a regression on windows XP.

git-svn-id: http://svn.boost.org/svn/boost/trunk@84946 b8fc166d-592f-0410-95f2-cb63ce0dd405
added new result_of mode that uses TR1 with a decltype fallback as suggested by Nathan Crookston; fixes #7753

git-svn-id: http://svn.boost.org/svn/boost/trunk@84949 b8fc166d-592f-0410-95f2-cb63ce0dd405