changed use of interoperable to say "if and only if"

also changed models section in indirect_iterator to mention
  iterator_traversal<>::type in addition to iterator_category


[SVN r21732]

libs/iterator

@@ -1 +1 @@
-Subproject commit 8a0e9a4fe51fc4629d5b8cc317962cf97db42545
+Subproject commit 2496402a8c2b476ebe83fc1719b6eafc3d282576