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/header/common/accept_encoding.rs

@@ -7,7 +7,7 @@ use header::shared;
 ///
 /// The `Accept-Encoding` header can be used by clients to indicate what
 /// response encodings they accept.
-#[deriving(Clone, PartialEq, Show)]
+#[derive(Clone, PartialEq, Show)]
 pub struct AcceptEncoding(pub Vec<shared::QualityItem<shared::Encoding>>);
 
 deref!(AcceptEncoding -> Vec<shared::QualityItem<shared::Encoding>>);