Merge iostreams, hash.

Including disallowing implicit casts to `hash_value`.


[SVN r63812]

hash/doc/changes.qbk

@@ -106,4 +106,12 @@
   Avoid hashing 0.5 and 0 to the same number.
 * Stop using deprecated `BOOST_HAS_*` macros.
 
+[h2 Boost 1.44.0]
+
+* Prevent implicit conversions when calling `hash_value`. If you find
+  that the new version breaks your code, you can enable the old
+  behaviour by defining `BOOST_HASH_ALLOW_IMPLICIT_CASTS` - although
+  I would recommend that you update your code to work with the new
+  version.
+
 [endsect]