Fixes a small issue that prevented the use of iterators of containers of incomplete types. Added iterators of incomp-types to unit-tests.

include/boost/container/detail/iterators.hpp

@@ -698,11 +698,16 @@ struct is_bidirectional_iterator<T, false>
    static const bool value = false;
 };
 
+template<class IINodeType>
+struct iiterator_node_value_type {
+  typedef typename IINodeType::value_type type;
+};
+
 template<class IIterator>
 struct iiterator_types
 {
    typedef typename IIterator::value_type                            it_value_type;
-   typedef typename it_value_type::value_type                        value_type;
+   typedef typename iiterator_node_value_type<it_value_type>::type   value_type;
    typedef typename std::iterator_traits<IIterator>::pointer         it_pointer;
    typedef typename std::iterator_traits<IIterator>::difference_type difference_type;
    typedef typename ::boost::intrusive::pointer_traits<it_pointer>::

include/boost/container/detail/tree.hpp

@@ -216,6 +216,11 @@ struct tree_node
    {  m_data = ::boost::move(v); }
 };
 
+template <class T, class VoidPointer, boost::container::tree_type_enum tree_type_value, bool OptimizeSize>
+struct iiterator_node_value_type< tree_node<T, VoidPointer, tree_type_value, OptimizeSize> > {
+  typedef T type;
+};
+
 template<class Node, class Icont>
 class insert_equal_end_hint_functor
 {

include/boost/container/list.hpp

@@ -81,6 +81,11 @@ struct list_node
    {  return this->m_data;   }
 };
 
+template <class T, class VoidPointer>
+struct iiterator_node_value_type< list_node<T,VoidPointer> > {
+  typedef T type;
+};
+
 template<class Allocator>
 struct intrusive_list_type
 {

include/boost/container/slist.hpp

@@ -87,6 +87,11 @@ struct slist_node
    {  return this->m_data;   }
 };
 
+template <class T, class VoidPointer>
+struct iiterator_node_value_type< slist_node<T,VoidPointer> > {
+  typedef T type;
+};
+
 template<class Allocator>
 struct intrusive_slist_type
 {