various bugfixes. filter_/transform_iterator were misusing enable_if

in a non-template context , and iterator_facade needed a forward
declaration for full conformance.


[SVN r19112]

libs/iterator

@@ -1 +1 @@
-Subproject commit 57a40c8cd2cf3d69a78a4293583bb1b93ef96e26
+Subproject commit 42e873e10c8d80dc990f939b760a1a9f5d5366a4