Widened the range of types that may be passed to is_convertible.

Extended is_base_and_derived to cope with ambiguous base classes
and non-public base classes.


[SVN r17146]

libs/type_traits

@@ -1 +1 @@
-Subproject commit 9ad8445156ac6e6bdcdd5c608971a31da558c703
+Subproject commit 524468f57940ac81744150e38b00b5ed5d3de95b