[boost] Review request: Require a SFINAE capable compiler

Hello, Several of the ancient compilers define BOOST_NO_SFINAE. The attached patch removes support for those versions of the compilers which are not capable of SFINAE. This bumps the compiler requirement to remove support for Borland 5.x, Metrowerks prior to 9.0, and SunPro prior to 5.7. Compilers based on EDG 238 are also affected, though it is unknown what those are. Ok to commit? Thanks, Steve.