Hash: Clean up some unit tests.

- Remove some unnecessary headers.
- Try to fix warning in enum tests.
- Compile tests + hash namespace in enum tests.


[SVN r80154]

test/hash_range_test.cpp

@@ -18,10 +18,7 @@ int main() {}
 #endif
 
 #include <boost/detail/lightweight_test.hpp>
-
 #include <boost/limits.hpp>
-#include <boost/mpl/assert.hpp>
-#include <boost/type_traits/is_base_and_derived.hpp>
 #include <vector>
 
 void hash_range_tests()