Unordered: Fix some portability issues in tests.

- Simplify mechanism for detecting traits of test allocators. There were
  some portability issues, but rather than fix them I've just gone for a
  simpler mechanism. Does mean that the relevant tests can't be run for
  other allocators.
- Fix a couple of unnecessary_copy_tests, whose results were the wrong
  way round.
- It appears that Visual C++ only implements RVO for implicitly defined
  copy constructors in debug mode, so adjust a move_test to account for
  the extra copies now that the copy constructors are explicitly
  defined.

[SVN r73798]

test/objects/test.hpp

@@ -284,6 +284,13 @@ namespace test
         {
             return tag_ != x.tag_;
         }
+
+        enum {
+            is_select_on_copy = false,
+            is_propagate_on_swap = false,
+            is_propagate_on_assign = false,
+            is_propagate_on_move = false
+        };
     };
 
     template <class T>