std: Add a new `env` module

This is an implementation of [RFC 578][rfc] which adds a new `std::env` module
to replace most of the functionality in the current `std::os` module. More
details can be found in the RFC itself, but as a summary the following methods
have all been deprecated:

[rfc]: https://github.com/rust-lang/rfcs/pull/578

* `os::args_as_bytes`   => `env::args`
* `os::args`            => `env::args`
* `os::consts`          => `env::consts`
* `os::dll_filename`    => no replacement, use `env::consts` directly
* `os::page_size`       => `env::page_size`
* `os::make_absolute`   => use `env::current_dir` + `join` instead
* `os::getcwd`          => `env::current_dir`
* `os::change_dir`      => `env::set_current_dir`
* `os::homedir`         => `env::home_dir`
* `os::tmpdir`          => `env::temp_dir`
* `os::join_paths`      => `env::join_paths`
* `os::split_paths`     => `env::split_paths`
* `os::self_exe_name`   => `env::current_exe`
* `os::self_exe_path`   => use `env::current_exe` + `pop`
* `os::set_exit_status` => `env::set_exit_status`
* `os::get_exit_status` => `env::get_exit_status`
* `os::env`             => `env::vars`
* `os::env_as_bytes`    => `env::vars`
* `os::getenv`          => `env::var` or `env::var_string`
* `os::getenv_as_bytes` => `env::var`
* `os::setenv`          => `env::set_var`
* `os::unsetenv`        => `env::remove_var`

Many function signatures have also been tweaked for various purposes, but the
main changes were:

* `Vec`-returning APIs now all return iterators instead
* All APIs are now centered around `OsString` instead of `Vec<u8>` or `String`.
  There is currently on convenience API, `env::var_string`, which can be used to
  get the value of an environment variable as a unicode `String`.

All old APIs are `#[deprecated]` in-place and will remain for some time to allow
for migrations. The semantics of the APIs have been tweaked slightly with regard
to dealing with invalid unicode (panic instead of replacement).

The new `std::env` module is all contained within the `env` feature, so crates
must add the following to access the new APIs:

    #![feature(env)]

[breaking-change]

1 files changed, 3 insertions, 4 deletions

diff --git a/src/test/bench/shootout-mandelbrot.rs b/src/test/bench/shootout-mandelbrot.rs
index 4a9c5a91dcf..ac32b584801 100644
--- a/src/test/bench/shootout-mandelbrot.rs
+++ b/src/test/bench/shootout-mandelbrot.rs
@@ -48,12 +48,12 @@ use std::simd::f64x2;
 use std::sync::Arc;
 use std::thread::Thread;
 
-const ITER: int = 50;
+const ITER: usize = 50;
 const LIMIT: f64 = 2.0;
-const WORKERS: uint = 16;
+const WORKERS: usize = 16;
 
 #[inline(always)]
-fn mandelbrot<W: old_io::Writer>(w: uint, mut out: W) -> old_io::IoResult<()> {
+fn mandelbrot<W: old_io::Writer>(w: usize, mut out: W) -> old_io::IoResult<()> {
     assert!(WORKERS % 2 == 0);
 
     // Ensure w and h are multiples of 8.
@@ -198,7 +198,6 @@ fn write_line(init_i: f64, vec_init_r: &[f64], res: &mut Vec<u8>) {
 
 fn main() {
     let args = os::args();
-    let args = args.as_slice();
     let res = if args.len() < 2 {
         println!("Test mode: do not dump the image because it's not utf8, \
                   which interferes with the test runner.");