Add code example to std::os::getenv for unix.
travis: Prevent timeouts with travis_wait

The most frequent failure for our travis builds is running into the timeout
limits when building the compiler itself. Building librustc takes a very long
amount of time, often hitting the 10 minutes with no output threshold that
travis imposes on us.

This commit switches the relevant `make` step to being wrapped in the
`travis_wait` command [1]. This command will print something once a minute so as
to not time out a build.

This will hopefully enable us to have fewer flaky builds on travis!

[1]: http://docs.travis-ci.com/user/build-timeouts/
Fixed weird grammar in lifetimes guide.
relicense shootout-meteor.rs

part of #14248, fix #14420

Removed @richo's contribution (outdated comment)

Quoting @brson: let's move forward with this one. The only
statement I'm missing is @richo's and it sounds like his was a
minor patch.
Update AUTHORS.txt
Adding examples and possible failures for getcwd.

For both window and unix platforms.
Remove a warning  (./configure: 1140: [: unexpected operator) when built with --disable-manage-submodules
Improve documentation on std::os::env.
How about a less cringe-worthy double-failure message?
auto merge of #14641 : darnuria/rust/add_documentation_to_std_os, r=alexcrichton

Just opening a pull request for adding code examples and documentation to std::os.

More to come soon.
mk: Move rust_test_helpers out of libstd

There's no need to distribute these ABI helpers for tests with the standard rust
distribution they're only needed for our tests.

Closes #2665
auto merge of #14653 : alexcrichton/rust/travis-opt, r=cmr

The most frequent failure for our travis builds is running into the timeout
limits when building the compiler itself. Building librustc takes a very long
amount of time, often hitting the 10 minutes with no output threshold that
travis imposes on us.

This commit switches the relevant `make` step to being wrapped in the
`travis_wait` command [1]. This command will print something once a minute so as
to not time out a build.

This will hopefully enable us to have fewer flaky builds on travis!

[1]: http://docs.travis-ci.com/user/build-timeouts/
auto merge of #14664 : reem/rust/lifetimes-guide-grammar, r=brson

Removed strange fragment-like thing in the intro.
auto merge of #14669 : TeXitoi/rust/relicense-shootout-meteor, r=brson

part of #14248, fix #14420

Removed @richo's contribution (outdated comment)

Quoting @brson: let's move forward with this one. The only
statement I'm missing is @richo's and it sounds like his was a
minor patch.
Fix documentation for `slice()`

Fixes https://github.com/mozilla/rust/issues/14577
Document BigInt's new and from_slice methods

Fixes https://github.com/mozilla/rust/issues/14639
Change to_str().to_string() to just to_str()
auto merge of #14667 : aochagavia/rust/pr2, r=huonw
auto merge of #14668 : aochagavia/rust/pr3, r=alexcrichton

Closes https://github.com/mozilla/rust/issues/14577
Closes https://github.com/mozilla/rust/issues/14639
auto merge of #14671 : aochagavia/rust/patch-1, r=alexcrichton