Merge type traits from Trunk:

* Adds uchar16_t and uchar32_t support.
* Adds is_copy_constructible trait.

[SVN r85474]

libs/type_traits

@@ -1 +1 @@
-Subproject commit 544307225b855b232f29365935eeb2606dce43fa
+Subproject commit 6d0830f46f51d79e80329910e5294f95b8d465bb