Added traits:

is_incrementable.hpp: checks whether ++x is well-formed

   pointee.hpp: value_type of iterators or smart pointers

   indirect_reference.hpp: reference type of iterators or smart pointers

indirect_iterator.hpp
indirect_iterator_member_types.cpp

   Use pointee/indirect_reference to select value/reference type.

iterator_concepts.hpp: Fixed interoperable test.  Hardly tests enough, but it's a start

minimum_category.hpp: Better error messages for vc6

indirect_iterator_test.cpp: Workarounds for compilers without SFINAE

static_assert_same.hpp: Informative error reports; added a macro.

zip_iterator_test.hpp: Added missing #include

Jamfile: made zip_iterator test pass with vc6/stlport

[SVN r21514]

include/boost/indirect_reference.hpp

@@ -0,0 +1,40 @@
+// Copyright David Abrahams 2004. Use, modification and distribution is
+// subject to the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+#ifndef INDIRECT_REFERENCE_DWA200415_HPP
+# define INDIRECT_REFERENCE_DWA200415_HPP
+
+// dereferenceable_traits provides access to the value_type and
+// reference of a Dereferenceable type.
+
+# include <boost/detail/is_incrementable.hpp>
+# include <boost/iterator/iterator_traits.hpp>
+# include <boost/type_traits/remove_cv.hpp>
+# include <boost/mpl/apply_if.hpp>
+
+namespace boost { 
+
+namespace detail
+{
+  template <class P>
+  struct smart_ptr_reference
+  {
+      typedef typename P::element_type& type;
+  };
+}
+
+template <class P>
+struct indirect_reference
+{
+    typedef typename remove_cv<P>::type stripped;
+    
+    typedef typename mpl::apply_if<
+        detail::is_incrementable<stripped>
+      , iterator_reference<stripped>
+      , detail::smart_ptr_reference<stripped>
+    >::type type;
+};
+  
+} // namespace boost
+
+#endif // INDIRECT_REFERENCE_DWA200415_HPP