Hash: Revert r81122. Refs #7470.

I'll get back to this later, it probably requires compiler specific changes.


[SVN r81124]

include/boost/functional/hash/detail/hash_float.hpp

@@ -210,7 +210,7 @@ namespace boost
         template <class T>
         inline std::size_t float_hash_value(T v)
         {
-            using namespace std::fpclassify;
+            using namespace std;
             switch (fpclassify(v)) {
             case FP_ZERO:
                 return 0;