std: Implement stdio for std::io

This is an implementation of RFC 899 and adds stdio functionality to the new
`std::io` module. Details of the API can be found on the RFC, but from a high
level:

* `io::{stdin, stdout, stderr}` constructors are now available. There are also
  `*_raw` variants for unbuffered and unlocked access.
* All handles are globally shared (excluding raw variants).
* The stderr handle is no longer buffered.
* All handles can be explicitly locked (excluding the raw variants).

The `print!` and `println!` machinery has not yet been hooked up to these
streams just yet. The `std::fmt::output` module has also not yet been
implemented as part of this commit.

src/libstd/sys/unix/mod.rs

@@ -63,6 +63,7 @@ pub mod time;
 pub mod timer;
 pub mod tty;
 pub mod udp;
+pub mod stdio;
 
 pub mod addrinfo {
     pub use sys_common::net::get_host_addresses;

src/libstd/sys/unix/stdio.rs

@@ -0,0 +1,52 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use prelude::v1::*;
+
+use io;
+use libc;
+use sys::fd::FileDesc;
+
+pub struct Stdin(());
+pub struct Stdout(());
+pub struct Stderr(());
+
+impl Stdin {
+    pub fn new() -> Stdin { Stdin(()) }
+
+    pub fn read(&self, data: &mut [u8]) -> io::Result<usize> {
+        let fd = FileDesc::new(libc::STDIN_FILENO);
+        let ret = fd.read(data);
+        fd.into_raw();
+        return ret;
+    }
+}
+
+impl Stdout {
+    pub fn new() -> Stdout { Stdout(()) }
+
+    pub fn write(&self, data: &[u8]) -> io::Result<usize> {
+        let fd = FileDesc::new(libc::STDOUT_FILENO);
+        let ret = fd.write(data);
+        fd.into_raw();
+        return ret;
+    }
+}
+
+impl Stderr {
+    pub fn new() -> Stderr { Stderr(()) }
+
+    pub fn write(&self, data: &[u8]) -> io::Result<usize> {
+        let fd = FileDesc::new(libc::STDERR_FILENO);
+        let ret = fd.write(data);
+        fd.into_raw();
+        return ret;
+    }
+}