rust-mode.el: Tweak syntax table

"_" should keep the default syntax class (symbol, not word). This
allows, e.g., `forward-word' to behave in the familiar way, jumping to
underscores within a function or variable name.
doc: adding example for implementations without traits
sys: reveal std::io representation to sys module

This commit adds a `AsInner` trait to `sys_common` and provides
implementations on many `std::io` types. This is a building block for
exposing platform-specific APIs that hook into `std::io` types.
libs: add std::os::unix module

The new `std::os::unix` module exposes several extension traits
for extracting file descriptors from `std::io` types.
libs: add std::os::windows module

The new `std::os::windows` module exposes several extension traits
for extracting file descriptors, sockets, and handles from `std::io`
types.
Search for implemented kinds recursively on Trait types. Fixes #15155 and #13155.
Require <T: Send> for AtomicOption

Fixes #19247.
Rename unwrap functions to into_inner

This change applies the conventions to unwrap listed in [RFC 430][rfc] to rename
non-failing `unwrap` methods to `into_inner`. This is a breaking change, but all
`unwrap` methods are retained as `#[deprecated]` for the near future. To update
code rename `unwrap` method calls to `into_inner`.

[rfc]: https://github.com/rust-lang/rfcs/pull/430
[breaking-change]

Closes #13159
cc #19091
save-analysis: two minor bugs
compiletest: extend syntax with support for choosing same line as previous line.
Add `node_to_user_string`, `node_to_string` variant that drops id from output.
rustdoc: Render associated types on traits and impls
rustdoc: render ast::QPath

Fix #18594
auto merge of #19250 : kmcallister/rust/atomicoption, r=alexcrichton

Fixes #19247.
auto merge of #19258 : nick29581/rust/dxr-minor, r=brson

r?
Merge libsync into libstd

This patch merges the `libsync` crate into `libstd`, undoing part of the
facade. This is in preparation for ultimately merging `librustrt`, as
well as the upcoming rewrite of `sync`.

Because this removes the `libsync` crate, it is a:

[breaking-change]

However, all uses of `libsync` should be able to reroute through
`std::sync` and `std::comm` instead.
Don't call drop in tcpstream docs

This suggests that you must call it, which is normally not what you want to do.
auto merge of #18818 : steveklabnik/rust/tcp_doc, r=alexcrichton

This suggests that you must call it, which is normally not what you want to do.

See here: http://www.reddit.com/r/rust/comments/2lpw9k/rust_irc_example_looking_for_feedback/clxnxxc?context=4
auto merge of #19021 : roysc/rust/emacs-pr, r=brson

"_" should keep the default syntax class (symbol, not word). This
allows, e.g., `forward-word' to behave in the familiar way, jumping to
underscores within a function or variable name.
std: Leak all statically allocated TLS keys

It turns out that rustrt::at_exit() doesn't actually occur after all pthread
threads have exited (nor does atexit()), so there's not actually a known point
at which we can deallocate these keys. It's not super critical that we do so,
however, because we're about to exit anyway!

Closes #19280