Merge unordered changes:

* Support emplace for all compilers.
 * Better configuration of C++0x features for when the appropriate headers
   aren't available.

Merged revisions 52393-52394,52397,52884-52885,53127,53255 via svnmerge from 
https://svn.boost.org/svn/boost/trunk

........
  r52393 | danieljames | 2009-04-14 18:23:37 +0100 (Tue, 14 Apr 2009) | 2 lines
  
  Implement full extract_key for compilers without SFINAE and variadic
  templates.
........
  r52394 | danieljames | 2009-04-14 18:23:51 +0100 (Tue, 14 Apr 2009) | 1 line
  
  Use emplace instead of insert in the backend as it's more appropriate.
........
  r52397 | danieljames | 2009-04-14 18:51:34 +0100 (Tue, 14 Apr 2009) | 1 line
  
  Add stream output to the count test helper for unordered.
........
  r52884 | danieljames | 2009-05-10 22:24:41 +0100 (Sun, 10 May 2009) | 19 lines
  
  Cherrypick some unordered container changes from sandbox. Not including
  anything which depends on the new move library.
  
  ------------------------------------------------------------------------
  r52746 | danieljames | 2009-05-03 11:12:30 +0100 (Sun, 03 May 2009) | 1 line
  
  Merge latest unordered container changes.
  ------------------------------------------------------------------------
  r52747 | danieljames | 2009-05-03 11:15:35 +0100 (Sun, 03 May 2009) | 4 lines
  
  Put the C++0x emplace implementations before the non-C++0x versions.
  
  I'm going to change the non-C++0x to be macro heavy emulations of the
  C++0x versions, so this will put the readable version first.
  ------------------------------------------------------------------------
  r52748 | danieljames | 2009-05-03 11:15:44 +0100 (Sun, 03 May 2009) | 1 line
  
  Refactor the unordered implementation a tad, to make implementing emplace less painful.
  ------------------------------------------------------------------------
........
  r52885 | danieljames | 2009-05-10 22:25:09 +0100 (Sun, 10 May 2009) | 1 line
  
  Merge emplace support for sandbox - but without move support.
........
  r53127 | danieljames | 2009-05-20 07:43:38 +0100 (Wed, 20 May 2009) | 1 line
  
  Better configuration for boost.unordered.
........
  r53255 | danieljames | 2009-05-25 20:45:06 +0100 (Mon, 25 May 2009) | 1 line
  
  Unordered change log.
........


[SVN r53257]

test/objects/exception.hpp

@@ -347,7 +347,7 @@ namespace exception
             detail::tracker.track_construct((void*) p, sizeof(T), tag_);
         }
 
-#if defined(BOOST_HAS_RVALUE_REFS) && defined(BOOST_HAS_VARIADIC_TMPL)
+#if defined(BOOST_UNORDERED_STD_FORWARD)
         template<class... Args> void construct(pointer p, Args&&... args) {
             UNORDERED_SCOPE(allocator::construct(pointer, Args&&...)) {
                 UNORDERED_EPOINT("Mock allocator construct function.");