Second try at merging emplace support.

Note that the previously rolled back commit was [53257], not [52357].

Merged revisions 52393-52394,52397,52884-52885,53255 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.
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  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.
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  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.
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  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.
  ------------------------------------------------------------------------
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  r52885 | danieljames | 2009-05-10 22:25:09 +0100 (Sun, 10 May 2009) | 1 line
  
  Merge emplace support for sandbox - but without move support.
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  r53255 | danieljames | 2009-05-25 20:45:06 +0100 (Mon, 25 May 2009) | 1 line
  
  Unordered change log.
........


[SVN r53328]

test/helpers/count.hpp

@@ -6,6 +6,8 @@
 #if !defined(BOOST_UNORDERED_TEST_HELPERS_COUNT_HEAD)
 #define BOOST_UNORDERED_TEST_HELPERS_COUNT_HEAD
 
+#include <iostream>
+
 namespace test {
     struct object_count {
         int instances;
@@ -36,6 +38,11 @@ namespace test {
         bool operator!=(object_count const& x) const {
             return !(*this == x);
         }
+        
+        friend std::ostream& operator<<(std::ostream& out, object_count const& c) {
+            out<<"[instances: "<<c.instances<<", constructions: "<<c.constructions<<"]";
+            return out;
+        }
     };
 
     template <class T>