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]

2 files changed, 0 insertions, 14 deletions

diff --git a/src/libstd/sys/common/mutex.rs b/src/libstd/sys/common/mutex.rs
index 9aea0fb3b31..0ca22826700 100644
--- a/src/libstd/sys/common/mutex.rs
+++ b/src/libstd/sys/common/mutex.rs
@@ -24,13 +24,6 @@ unsafe impl Sync for Mutex {}
 pub const MUTEX_INIT: Mutex = Mutex(imp::MUTEX_INIT);
 
 impl Mutex {
-    /// Creates a newly initialized mutex.
-    ///
-    /// Behavior is undefined if the mutex is moved after the first method is
-    /// called on the mutex.
-    #[inline]
-    pub unsafe fn new() -> Mutex { Mutex(imp::Mutex::new()) }
-
     /// Lock the mutex blocking the current thread until it is available.
     ///
     /// Behavior is undefined if the mutex has been moved between this and any
diff --git a/src/libstd/sys/common/rwlock.rs b/src/libstd/sys/common/rwlock.rs
index df016b9e293..fe374e1fd78 100644
--- a/src/libstd/sys/common/rwlock.rs
+++ b/src/libstd/sys/common/rwlock.rs
@@ -21,13 +21,6 @@ pub struct RWLock(imp::RWLock);
 pub const RWLOCK_INIT: RWLock = RWLock(imp::RWLOCK_INIT);
 
 impl RWLock {
-    /// Creates a new instance of an RWLock.
-    ///
-    /// Usage of an RWLock is undefined if it is moved after its first use (any
-    /// function calls below).
-    #[inline]
-    pub unsafe fn new() -> RWLock { RWLock(imp::RWLock::new()) }
-
     /// Acquire shared access to the underlying lock, blocking the current
     /// thread to do so.
     ///