This change introduces a Dockerfile and script which builds a complete
Fuchsia toolchain which can be used to build Rust distribution for
Fuchsia. We only support cross-compiling at the moment, hence only
setting the target.

travis: Fuchsia builder

This change introduces a Dockerfile and script which builds a complete
Fuchsia toolchain which can be used to build Rust distribution for
Fuchsia. We only support cross-compiling at the moment, hence only
setting the target.

…=eddyb

librustc error_reporting.rs cleanup.

Read some code in librustc, mainly in error_reporting.rs, and cleaned up some things along the way. I recommend looking at each commit individually or looking at the [whitespace insensitive diff](https://github.com/rust-lang/rust/pull/39977/files?w=1).

Add compile fail test for unboxed_closures feature

Hello, this is my first contribution to rust.
Issue rust-lang#39059.

Fix nightly-only experimental API display

Before:

<img width="1440" alt="screen shot 2017-02-23 at 12 53 09" src="https://cloud.githubusercontent.com/assets/3050060/23258119/0c9cf6f2-f9c7-11e6-9989-15b4346dade0.png">

After:

<img width="1440" alt="screen shot 2017-02-23 at 12 51 40" src="https://cloud.githubusercontent.com/assets/3050060/23258076/e6881118-f9c6-11e6-826c-442a73502b59.png">

r? @frewsxcv

Fix a typo