fix(rustup): update io import, Writer::write

Make it build with the latest rust-nightly (2015-01-27)

Renamed io import to old_io.
Renamed Writer::write to Writer::write_all

src/header/common/authorization.rs

@@ -141,7 +141,7 @@ impl FromStr for Basic {
 
 #[cfg(test)]
 mod tests {
-    use std::io::MemReader;
+    use std::old_io::MemReader;
     use super::{Authorization, Basic};
     use super::super::super::{Headers};