Remove Real trait and move methods into Float

This is part of the effort to simplify `std::num`, as tracked in issue #10387.
Clean up std::task docs, make TaskBuilder a real builder

Delete all the documentation from std::task that references linked
failure.

Tweak TaskBuilder to be more builder-like. .name() is now .named() and
.add_wrapper() is now .with_wrapper(). Remove .watched() and
.unwatched() as they didn't actually do anything.
Update clients of the TaskBuilder API
Implement Unix domain sockets in libnative
Move unix pipes implementation to pipe_unix.rs

The windows named pipes implementation will have almost nothing to do with unix
pipes, so I think it's best if they live in separate files.
Implement named pipes for windows, touch up unix

* Implementation of pipe_win32 filled out for libnative
* Reorganize pipes to be clone-able
* Fix a few file descriptor leaks on error
* Factor out some common code into shared functions
* Make use of the if_ok!() macro for less indentation

Closes #11201
Remove Freeze bounds from sync::MutexArc

With Rc no longer trying to statically prevent cycles (and thus no
longer using the Freeze bound), it seems appropriate to remove that
restriction from MutexArc as well.
Update tasks guide: SharedChan as been removed

The code examples are up to date, but the surrounding explanations are not.
Added more scripts to tidy check
Remove the compile-fail test that's now obsolete
backticks for syntax elements
Spellcheck library docs.
Fix a deadlock in channels, again.

This deadlock was caused when the channel was closed at just the right time, so
the extra `self.cnt.fetch_add` actually should have preserved the DISCONNECTED
state of the channel. by modifying this the channel entered a state such that
the port would never succeed in dropping.

This also moves the increment of self.steals until after the MAX_STEALS block.
The reason for this is that in 'fn recv()' the steals variable is decremented
immediately after the try_recv(), which could in theory set steals to -1 if it
was previously set to 0 in try_recv().

Closes #12340
auto merge of #12352 : alexcrichton/rust/fix-master, r=brson

This deadlock was caused when the channel was closed at just the right time, so
the extra `self.cnt.fetch_add` actually should have preserved the DISCONNECTED
state of the channel. by modifying this the channel entered a state such that
the port would never succeed in dropping.

This also moves the increment of self.steals until after the MAX_STEALS block.
The reason for this is that in 'fn recv()' the steals variable is decremented
immediately after the try_recv(), which could in theory set steals to -1 if it
was previously set to 0 in try_recv().

Closes #12340
Fix a segfault in the rustuv tests

The details can be found in the comments I added to the test, but the gist of it
is that capturing output injects rescheduling a green task on failure, which
wasn't desired for the test in question.

cc #12340
Updated metadata::creader::resolve_crate_deps to use the correct span. Clarified error message when an external crate's dependency is missing. Closes #2404.
auto merge of #12146 : gentlefolk/rust/issue-2404, r=alexcrichton

Addresses FIXME described in issue #2404
auto merge of #12232 : kballard/rust/taskbuilder-is-a-builder, r=alexcrichton

Delete all the documentation from std::task that references linked
failure.

Tweak TaskBuilder to be more builder-like. `.name()` is now `.named()` and
`.add_wrapper()` is now `.with_wrapper()`. Remove `.watched()` and
`.unwatched()` as they didn't actually do anything.

Closes #6399.
auto merge of #12243 : dguenther/rust/extend-tidy, r=alexcrichton

Extends the license and formatting check to `*.js` files in `src/doc` and `*.sh`, `*.pl`, `*.c`, and `*.h` files in `src/etc`. As best as I could tell, these files should be covered under the Rust project license.

cc @brson: Do any other scripts need a license? I'd like to double-check that this PR closes #4534.
Test ordering of glue_drop and glue_takew in self-re-assignment. Closes #3290.