Some of this was there for older compilers, some is just premature
generalization. There's still too much metaprogramming, but these are things
that are relatively easy to remove.
[SVN r79356]
Only for compilers with SFINAE expressions and recent versions of Visual
C++. Also fix Visual C++ 8, and use BOOST_UNORDERED_ prefix for all
macros.
[SVN r74106]