Publicise types/add #[allow(visible_private_types)] to a variety of places.

There's a lot of these types in the compiler libraries, and a few of the
older or private stdlib ones. Some types are obviously meant to be
public, others not so much.

src/librustc/lib.rs

@@ -30,6 +30,8 @@ This API is completely unstable and subject to change.
 #[feature(macro_rules, globs, struct_variant, managed_boxes)];
 #[feature(quote)];
 
+#[allow(visible_private_types)];
+
 extern crate extra;
 extern crate flate;
 extern crate arena;