Unordered: Reorganization to use void pointers and other things.

Helps allocators which can't use incomplete pointers, and avoid using
base pointers where that might not be possible.  And some other
reorganization. Storing arguments to emplace in a structure when
variadic template parameters aren't available. Changed some of the odd
design for working with older compilers.

[SVN r74742]

test/unordered/unnecessary_copy_tests.cpp

@@ -245,9 +245,11 @@ namespace unnecessary_copy_tests
         x.emplace();
 #if defined(BOOST_UNORDERED_STD_FORWARD_MOVE)
         COPY_COUNT(1); MOVE_COUNT(0);
-#else
+#elif !defined(BOOST_NO_RVALUE_REFERENCES)
         // source_cost doesn't make much sense here, but it seems to fit.
         COPY_COUNT(1); MOVE_COUNT(source_cost);
+#else
+        COPY_COUNT(1); MOVE_COUNT(1 + source_cost);
 #endif
 #endif
 
@@ -357,7 +359,6 @@ namespace unnecessary_copy_tests
     (defined(__GNUC__) && __GNUC__ == 4 && __GNUC_MINOR__ > 2) || \
     (defined(BOOST_MSVC) && BOOST_MSVC >= 1600 ) || \
     (!defined(__GNUC__) && !defined(BOOST_MSVC))
-
         count_copies part;
         reset();
         std::pair<count_copies const&, count_copies const&> a_ref(part, part);