Prevent unsized types being stored in variables

Closes #13376.
auto merge of #13715 : nick29581/rust/unsized-assign2, r=nikomatsakis

Closes #13376.
Update libuv

This update brings a few months of changes, but primarily a fix for the
following situation.

When creating a handle to stdin, libuv used to set the stdin handle to
nonblocking mode. This would end up affect this stdin handle across all
processes that shared it, which mean that stdin become nonblocking for everyone
using the same stdin. On linux, this also affected *stdout* because stdin/stdout
roughly point at the same thing.

This problem became apparent when running the test suite manually on a local
computer. The stdtest suite (running with libgreen) would set stdout to
nonblocking mode (as described above), and then the next test suite would always
fail for a printing failure (because stdout was returning EAGAIN).

This has been fixed upstream, joyent/libuv@342e8c, and this update pulls in this
fix. This also brings us in line with a recently upstreamed libuv patch.

Closes #13336
Closes #13355
test: Add an option to not capture output

A new flag to the test runner, --nocapture, can be passed to instruct that the
output of tests should not be captured by default. The behavior can also be
triggered via a RUST_TEST_NOCAPTURE environment variable being set.

Closes #13374
auto merge of #13619 : alexcrichton/rust/update-libuv, r=brson

This update brings a few months of changes, but primarily a fix for the
following situation.

When creating a handle to stdin, libuv used to set the stdin handle to
nonblocking mode. This would end up affect this stdin handle across all
processes that shared it, which mean that stdin become nonblocking for everyone
using the same stdin. On linux, this also affected *stdout* because stdin/stdout
roughly point at the same thing.

This problem became apparent when running the test suite manually on a local
computer. The stdtest suite (running with libgreen) would set stdout to
nonblocking mode (as described above), and then the next test suite would always
fail for a printing failure (because stdout was returning EAGAIN).

This has been fixed upstream, joyent/libuv@342e8c, and this update pulls in this
fix. This also brings us in line with a recently upstreamed libuv patch.

Closes #12827
Closes #13336
Closes #13355
fix O(n^2) perf bug for std::io::fs::walk_dir

The `walk_dir` iterator was simulating a queue using a vector (in particular, using `shift`),
leading to O(n^2) performance. Since the order was not well-specified (see issue #13411),
the simplest fix is to use the vector as a stack (and thus yield a depth-first traversal).
This patch does exactly that.  It leaves the order as originally specified -- "some top-down
order" -- and adds a test to ensure a top-down traversal.

Note that the underlying `readdir` function does not specify any particular order, nor
does the system call it uses.

Closes #13411.
auto merge of #13706 : alexcrichton/rust/test-nocapture, r=brson

A new flag to the test runner, --nocapture, can be passed to instruct that the
output of tests should not be captured by default. The behavior can also be
triggered via a RUST_TEST_NOCAPTURE environment variable being set.

Closes #13374
auto merge of #13720 : aturon/rust/walk_dir-perf, r=alexcrichton

The `walk_dir` iterator was simulating a queue using a vector (in particular, using `shift`),
leading to O(n^2) performance. Since the order was not well-specified (see issue #13411),
the simplest fix is to use the vector as a stack (and thus yield a depth-first traversal).
This patch does exactly that, and adds a test checking for depth-first behavior.

Note that the underlying `readdir` function does not specify any particular order, nor
does the system call it uses.

Closes #13411.
Add a regex crate to the Rust distribution.

Also adds a regex_macros crate, which provides natively compiled
regular expressions with a syntax extension.

Closes #3591.

RFC: 0007-regexps