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/librustuv/lib.rs

@@ -41,6 +41,7 @@ via `close` and `delete` methods.
 
 #[feature(macro_rules)];
 #[deny(unused_result, unused_must_use)];
+#[allow(visible_private_types)];
 
 #[cfg(test)] extern crate green;