auto merge of #12522 : erickt/rust/hash, r=alexcrichton

This patch series does a couple things:

* replaces manual `Hash` implementations with `#[deriving(Hash)]`
* adds `Hash` back to `std::prelude`
* minor cleanup of whitespace and variable names.

src/libstd/lib.rs

@@ -151,7 +151,6 @@ pub mod container;
 pub mod default;
 pub mod any;
 
-
 /* Common data structures */
 
 pub mod option;