More Rust updates:

- Some stray deriving -> derive changes
- use::{mod} -> use::{self}
- fmt.write -> fmt.write_str

This does not catch the last case of fmt.write_str in the
Show impl of a Header Item. This will need to be changed
separately.

benches/client_mock_tcp.rs

@@ -4,7 +4,7 @@ extern crate hyper;
 
 extern crate test;
 
-use std::fmt::{mod, Show};
+use std::fmt::{self, Show};
 use std::str::from_str;
 use std::io::{IoResult, MemReader};
 use std::io::net::ip::SocketAddr;