…[macro_reexport]`)

and macros 2.0 exports (`pub use` macro re-exports and `pub macro` (once implemented)
at the crate root.

It now follows rustc release trains

Adds a test for issue rust-lang#31946 which was fixed a while ago.

…orts, r=nrc

Forbid conflicts between macros 1.0 exports and macros 2.0 exports

This PR forbids for conflicts between `#[macro_export]`/`#[macro_reexport]` macro exports and `pub use` macro exports. For example,
```rust
// crate A:
pub use macros::foo;
//^ This is allowed today, will be forbidden by this PR.

// crate B:
extern crate A; // This triggers a confusing error today.
use A::foo; // This could refer to refer to either macro export in crate A.
```

r? @nrc

rustbuild: Don't hardcode 'nightly' for Cargo

It now follows rustc release trains. I also had to land this commit on beta (rust-lang@0a27a87) before rust-lang#40484 could land, so this is basically just a forward port (if you will) of that commit to master.

add test for nested macro def (rust-lang#31946)

Adds a test for issue rust-lang#31946 which was fixed in 1.12.0.

Closes rust-lang#31946.

Update gcc used for dist-x86-linux builds

GCC 4.7 is too old to build LLVM 4.0, so this PR updates to 4.8.

r? @alexcrichton (I'll ping you again once travis is green and the test commit is removed).

…e, r=frewsxcv

Add docs for sort_unstable to unstable book

Tracking issue for the feature: rust-lang#40585

r? @steveklabnik

…ype-formatting, r=frewsxcv

Add whitespace around "=" in assoc items

Part of rust-lang#40641.

r? @rust-lang/docs

Before:

<img width="1440" alt="screen shot 2017-03-20 at 22 42 34" src="https://cloud.githubusercontent.com/assets/3050060/24123102/89181d8c-0dbe-11e7-897c-841497cf7001.png">

After:

<img width="1440" alt="screen shot 2017-03-20 at 22 42 36" src="https://cloud.githubusercontent.com/assets/3050060/24123118/8dec176e-0dbe-11e7-9759-cabbd062a4c2.png">

…wsxcv

Fix invalid linking in iter docs

r? @rust-lang/docs

…uation, r=bstrie

str: Make docs consistently punctuated

Every so slightly pointless one character PR, but this was driving me nuts while reading the docs a moment ago (all the [other public structs](https://doc.rust-lang.org/std/str/index.html#structs) have descriptions that end in a full-stop).