Unordered: Merge from trunk

- Remove use of BOOST_DEDUCED_TYPENAME and BOOST_UNORDERED_PAIR_CAST, it's
  unlikely that the compilers which require them will be able to cope with the
  new version of unordered.
- Use the old equality algorithm if BOOST_UNORDERED_DEPRECATED_EQUALITY is
  defined.
- Use SFINAE to control which overloads of `construct_impl` are available.
  Fixes problems with differing overload resolution on different compilers.
- Support for piecewise pair construction.
- Only support the old variadic pair construction when
  BOOST_UNORDERED_DEPRECATED_PAIR_CONSTRUCT is defined (also fixed some bugs).
- Avoid instantiating BOOST_RV_REF for non-classes.
- Support optional allocator member functions for compilers with SFINAE
  expressions and Visual C++ 9.0/10.0
- Follow boost macro naming conventions.
- Improved portability for `allocator_traits` emulation.

Current compiler support:

- Full support for GCC 4.4+, Visual C++ 9.0+, Clang.
- All other compilers odn't support optional allocator members.
- No other errors for GCC 3.4.6+, Visual C++ 8.0, Intel, Pathscale.
- Visual Age has a compile error if `select_on_container_copy_construction`
  isn't `const` (it should ignore it).
- `select_on_container_copy_construction` detection doesn't work on Sun.
- `unnecessary_copy_tests` is failling for vacpp on AIX, but not on linux.
- Warnings causing failures for Visual C++ with STLport and WM5.


[SVN r74234]

doc/unordered.qbk

@@ -3,7 +3,7 @@
  / file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) ]
 
 [library Boost.Unordered
-    [quickbook 1.4]
+    [quickbook 1.5]
     [authors [James, Daniel]]
     [copyright 2003 2004 Jeremy B. Maitin-Shepard]
     [copyright 2005 2006 2007 2008 Daniel James]