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.

src/client/request.rs

@@ -6,7 +6,7 @@ use url::Url;
 use method;
 use method::Method::{Get, Post, Delete, Put, Patch, Head, Options};
 use header::Headers;
-use header::common::{mod, Host};
+use header::common::{self, Host};
 use net::{NetworkStream, NetworkConnector, HttpConnector, Fresh, Streaming};
 use http::{HttpWriter, LINE_ENDING};
 use http::HttpWriter::{ThroughWriter, ChunkedWriter, SizedWriter, EmptyWriter};