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_function_pointer_test.cpp

@@ -12,10 +12,6 @@
 #endif
 
 #include <boost/detail/lightweight_test.hpp>
-
-#include <boost/mpl/assert.hpp>
-#include <boost/type_traits/is_base_and_derived.hpp>
-
 #include "./compile_time.hpp"
 
 void void_func1() { static int x = 1; ++x; }