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

examples/hello.rs

@@ -1,14 +1,14 @@
 #![allow(unstable)]
 extern crate hyper;
 
-use std::io::net::ip::Ipv4Addr;
+use std::old_io::net::ip::Ipv4Addr;
 use hyper::server::{Request, Response};
 
 static PHRASE: &'static [u8] = b"Hello World!";
 
 fn hello(_: Request, res: Response) {
     let mut res = res.start().unwrap();
-    res.write(PHRASE).unwrap();
+    res.write_all(PHRASE).unwrap();
     res.end().unwrap();
 }