Update all common headers for the new Header trait split

src/header/common/host.rs

@@ -1,4 +1,4 @@
-use header::Header;
+use header::{Header, HeaderFormat};
 use Port;
 use std::fmt::{mod, Show};
 use super::util::from_one_raw_str;
@@ -61,7 +61,9 @@ impl Header for Host {
             })
         })
     }
+}
 
+impl HeaderFormat for Host {
     fn fmt_header(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
         match self.port {
             None | Some(80) | Some(443) => self.hostname.fmt(fmt),