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/set_cookie.rs

@@ -1,5 +1,5 @@
 use header::{Header, HeaderFormat};
-use std::fmt::{mod, Show};
+use std::fmt::{self, Show};
 use std::str::from_utf8;
 
 use cookie::Cookie;
@@ -52,7 +52,7 @@ impl HeaderFormat for SetCookie {
     fn fmt_header(&self, f: &mut fmt::Formatter) -> fmt::Result {
         for (i, cookie) in self.0.iter().enumerate() {
             if i != 0 {
-                try!(f.write(b"\r\nSet-Cookie: "));
+                try!(f.write_str("\r\nSet-Cookie: "));
             }
             try!(cookie.fmt(f));
         }