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/unordered/unnecessary_copy_tests.cpp

@@ -201,9 +201,9 @@ namespace unnecessary_copy_tests
         COPY_COUNT(1); MOVE_COUNT(0);
         x.emplace(boost::move(a));
 #if defined(BOOST_NO_RVALUE_REFERENCES)
-        COPY_COUNT(1); MOVE_COUNT(1);
-#else
         COPY_COUNT(2); MOVE_COUNT(0);
+#else
+        COPY_COUNT(1); MOVE_COUNT(1);
 #endif
     }
 
@@ -227,11 +227,11 @@ namespace unnecessary_copy_tests
         reset();
         x.emplace();
 #if defined(BOOST_UNORDERED_STD_FORWARD_MOVE)
+        COPY_COUNT(1); MOVE_COUNT(0);
+#else
         // TODO: I think that in this case the move could be delayed until
         // after checking for a collision, giving MOVE_COUNT(0).
         COPY_COUNT(1); MOVE_COUNT(1);
-#else
-        COPY_COUNT(1); MOVE_COUNT(0);
 #endif
 
         //