remove dead link to rustpkg documentation
Tweak test name and make it more specific
Add ignore-cross-compile directive for compiletest

Loadable syntax extensions don't work when cross compiling (see #12102), so the
fourcc tests all need to be ignored. They're valuable tests, so they shouldn't
be outright ignored, so they're now flagged with ignore-cross-compile
Added examples for converting vectors of u8 into strings. Also fixed some styling
Fixed fourcc example doc
Shuffle around ownership in concurrent queues

Beforehand, using a concurrent queue always mandated that the "shared state" be
stored internally to the queues in order to provide a safe interface. This isn't
quite as flexible as one would want in some circumstances, so instead this
commit moves the queues to not containing the shared state.

The queues no longer have a "default useful safe" interface, but rather a
"default safe" interface (minus the useful part). The queues have to be shared
manually through an Arc or some other means. This allows them to be a little
more flexible at the cost of a usability hindrance.

I plan on using this new flexibility to upgrade a channel to a shared channel
seamlessly.
Rewrite channels yet again for upgradeability

This, the Nth rewrite of channels, is not a rewrite of the core logic behind
channels, but rather their API usage. In the past, we had the distinction
between oneshot, stream, and shared channels, but the most recent rewrite
dropped oneshots in favor of streams and shared channels.

This distinction of stream vs shared has shown that it's not quite what we'd
like either, and this moves the `std::comm` module in the direction of "one
channel to rule them all". There now remains only one Chan and one Port.

This new channel is actually a hybrid oneshot/stream/shared channel under the
hood in order to optimize for the use cases in question. Additionally, this also
reduces the cognitive burden of having to choose between a Chan or a SharedChan
in an API.

My simple benchmarks show no reduction in efficiency over the existing channels
today, and a 3x improvement in the oneshot case. I sadly don't have a
pre-last-rewrite compiler to test out the old old oneshots, but I would imagine
that the performance is comparable, but slightly slower (due to atomic reference
counting).

This commit also brings the bonus bugfix to channels that the pending queue of
messages are all dropped when a Port disappears rather then when both the Port
and the Chan disappear.
Test fixes and rebase conflicts
auto merge of #11578 : alexcrichton/rust/chan-changes, r=brson

The user-facing API-level change of this commit is that `SharedChan` is gone and `Chan` now has `clone`. The major parts of this patch are the internals which have changed.

Channels are now internally upgraded from oneshots to streams to shared channels depending on the use case. I've noticed a 3x improvement in the oneshot case and very little slowdown (if any) in the stream/shared case.

This patch is mostly a reorganization of the `std::comm` module, and the large increase in code is from either dispatching to one of 3 impls or the duplication between the stream/shared impl (because they're not entirely separate).

The `comm` module is now divided into `oneshot`, `stream`, `shared`, and `select` modules. Each module contains the implementation for that flavor of channel (or the select implementation for select).

Some notable parts of this patch

* Upgrades are done through a semi-ad-hoc scheme for oneshots and messages for streams
* Upgrades are processed ASAP and have some interesting interactions with select
* send_deferred is gone because I expect the mutex to land before this
* Some of stream/shared is straight-up duplicated, but I like having the distinction between the two modules
* Select got a little worse, but it's still "basically limping along"
* This lumps in the patch of deallocating the queue backlog on packet drop
* I'll rebase this on top of the "more errors from try_recv" patch once it lands (all the infrastructure is here already)

All in all, this shouldn't be merged until the new mutexes are merged (because send_deferred wasn't implemented).

Closes #11351
Finalize the Seek API

This adopts the rules posted in #10432:

1. If a seek position is negative, then an error is generated
2. Seeks beyond the end-of-file are allowed. Future writes will fill the gap
   with data and future reads will return errors.
3. Seeks within the bounds of a file are fine.

Closes #10432
auto merge of #12184 : JeremyLetang/rust/rustpkg-link, r=alexcrichton
auto merge of #12185 : nikomatsakis/rust/issue-12033-tweak-test, r=alexchrichton
auto merge of #12190 : alexcrichton/rust/fix-snap-again, r=brson

Loadable syntax extensions don't work when cross compiling (see #12102), so the
fourcc tests all need to be ignored. They're valuable tests, so they shouldn't
be outright ignored, so they're now flagged with ignore-cross-compile
auto merge of #12194 : WebeWizard/rust/master, r=cmr
doc: rename 'nil' to 'unit' when describing `()`
Removed ty_type (previously used to represent *tydesc).
auto merge of #12180 : eddyb/rust/rm-ty_type, r=nikomatsakis
auto merge of #12196 : dguenther/rust/fix-fourcc-example, r=alexcrichton

Cleans up a few issues with `fourcc`:
* Corrects the endianness in the docs example
* Removes `#[cfg(not(test))]` (bors might not build this on Windows. If the build fails, I'll re-add it)
* Adds a FIXME referencing the LLVM assert issue we encountered with bors builds on Windows (Same error as #10872)
auto merge of #12204 : alexcrichton/rust/seek, r=pcwalton

This adopts the rules posted in #10432:

1. If a seek position is negative, then an error is generated
2. Seeks beyond the end-of-file are allowed. Future writes will fill the gap
   with data and future reads will return errors.
3. Seeks within the bounds of a file are fine.

Closes #10432
Expose whether event loops have active I/O

The green scheduler can optimize its runtime based on this by deciding to not go
to sleep in epoll() if there is no active I/O and there is a task to be stolen.

This is implemented for librustuv by keeping a count of the number of tasks
which are currently homed. If a task is homed, and then performs a blocking I/O
operation, the count will be nonzero while the task is blocked. The homing count
is intentionally 0 when there are I/O handles, but no handles currently blocked.
The reason for this is that epoll() would only be used to wake up the scheduler
anyway.

The crux of this change was to have a `HomingMissile` contain a mutable borrowed
reference back to the `HomeHandle`. The rest of the change was just dealing with
this fallout. This reference is used to decrement the homed handle count in a
HomingMissile's destructor.

Also note that the count maintained is not atomic because all of its
increments/decrements/reads are all on the same I/O thread.