Put the minimum amount of implementation in the same namespace as the 'using namespace' directives in order to avoid Visual C++ 8 bug.

[SVN r54024]

hash/test/namespace_fail_test.cpp

@@ -0,0 +1,6 @@
+#include <list>
+#include <boost/functional/hash/detail/float_functions.hpp>
+
+typedef list<int> foo;
+
+int main() {}