This change makes the compiler no longer infer whether types (structures
and enumerations) implement the `Copy` trait (and thus are implicitly
copyable). Rather, you must implement `Copy` yourself via `impl Copy for
MyType {}`.

A new warning has been added, `missing_copy_implementations`, to warn
you if a non-generic public type has been added that could have
implemented `Copy` but didn't.

For convenience, you may *temporarily* opt out of this behavior by using
`#![feature(opt_out_copy)]`. Note though that this feature gate will never be
accepted and will be removed by the time that 1.0 is released, so you should
transition your code away from using it.

This breaks code like:

    #[deriving(Show)]
    struct Point2D {
        x: int,
        y: int,
    }

    fn main() {
        let mypoint = Point2D {
            x: 1,
            y: 1,
        };
        let otherpoint = mypoint;
        println!("{}{}", mypoint, otherpoint);
    }

Change this code to:

    #[deriving(Show)]
    struct Point2D {
        x: int,
        y: int,
    }

    impl Copy for Point2D {}

    fn main() {
        let mypoint = Point2D {
            x: 1,
            y: 1,
        };
        let otherpoint = mypoint;
        println!("{}{}", mypoint, otherpoint);
    }

This is the backwards-incompatible part of #13231.

Part of RFC #3.

[breaking-change]

This breaks code that referred to variant names in the same namespace as
their enum. Reexport the variants in the old location or alter code to
refer to the new locations:

```
pub enum Foo {
    A,
    B
}

fn main() {
    let a = A;
}
```
=>
```
pub use self::Foo::{A, B};

pub enum Foo {
    A,
    B
}

fn main() {
    let a = A;
}
```
or
```
pub enum Foo {
    A,
    B
}

fn main() {
    let a = Foo::A;
}
```

[breaking-change]

No longer does anything.

This removes all remnants of `@` pointers from rustc. Additionally, this removes
the `GC` structure from the prelude as it seems odd exporting an experimental
type in the prelude by default.

Closes #14193
[breaking-change]

This commit moves all logging out of the standard library into an external
crate. This crate is the new crate which is responsible for all logging macros
and logging implementation. A few reasons for this change are:

* The crate map has always been a bit of a code smell among rust programs. It
  has difficulty being loaded on almost all platforms, and it's used almost
  exclusively for logging and only logging. Removing the crate map is one of the
  end goals of this movement.

* The compiler has a fair bit of special support for logging. It has the
  __log_level() expression as well as generating a global word per module
  specifying the log level. This is unfairly favoring the built-in logging
  system, and is much better done purely in libraries instead of the compiler
  itself.

* Initialization of logging is much easier to do if there is no reliance on a
  magical crate map being available to set module log levels.

* If the logging library can be written outside of the standard library, there's
  no reason that it shouldn't be. It's likely that we're not going to build the
  highest quality logging library of all time, so third-party libraries should
  be able to provide just as high-quality logging systems as the default one
  provided in the rust distribution.

With a migration such as this, the change does not come for free. There are some
subtle changes in the behavior of liblog vs the previous logging macros:

* The core change of this migration is that there is no longer a physical
  log-level per module. This concept is still emulated (it is quite useful), but
  there is now only a global log level, not a local one. This global log level
  is a reflection of the maximum of all log levels specified. The previously
  generated logging code looked like:

    if specified_level <= __module_log_level() {
        println!(...)
    }

  The newly generated code looks like:

    if specified_level <= ::log::LOG_LEVEL {
        if ::log::module_enabled(module_path!()) {
            println!(...)
        }
    }

  Notably, the first layer of checking is still intended to be "super fast" in
  that it's just a load of a global word and a compare. The second layer of
  checking is executed to determine if the current module does indeed have
  logging turned on.

  This means that if any module has a debug log level turned on, all modules
  with debug log levels get a little bit slower (they all do more expensive
  dynamic checks to determine if they're turned on or not).

  Semantically, this migration brings no change in this respect, but
  runtime-wise, this will have a perf impact on some code.

* A `RUST_LOG=::help` directive will no longer print out a list of all modules
  that can be logged. This is because the crate map will no longer specify the
  log levels of all modules, so the list of modules is not known. Additionally,
  warnings can no longer be provided if a malformed logging directive was
  supplied.

The new "hello world" for logging looks like:

    #[phase(syntax, link)]
    extern crate log;

    fn main() {
        debug!("Hello, world!");
    }

Who doesn't like a massive renaming?