emacs: Don't overwrite font lock for attributes

This addresses the font lock regression introduced by the earlier pull
request #14818 - attributes are no longer be highligted inside of comments
and strings.

Also add some font lock test infrastructure and some tests for attribute
font locking.
emacs: Add shebang to test script
emacs: Remove outdated references to ~ in tests
Wrap debuginfo.rs at 80 columns.

Plus a few other misc style things.
change ~[] -> Vec for collect()

This updates the documentation for result::collect() and
option::collect() to use the new-style syntax for vectors, instead of
the old ~[].

Also updates the code blocks for these docs so they will be tested
automatically.

closes #14991
auto merge of #14992 : nathantypanski/rust/collect-docs, r=huonw

This updates the documentation for result::collect() and
option::collect() to use the new-style syntax for owned pointers and
vectors.

closes #14991
fix signatures of mmap-related functions from libc
rustdoc: Fix testing indented code blocks

The collapse/unindent passes were run in the wrong order, generating different
markdown for indented tests.
rustdoc: Don't inject `extern crate std`.

No need to duplicate the compiler's work!

Closes #14999
std: Remove dual export of `Show`

Closes #14996
auto merge of #14994 : nick29581/rust/comments, r=bstrie

Plus a few other misc style things.
auto merge of #15000 : alexcrichton/rust/fix-rustdoc-tests, r=huonw

Commits have the descriptions.
auto merge of #14990 : tomjakubowski/rust/emacs-fix-attribute-highlight, r=pnkfelix

This addresses the font lock regression introduced by the earlier pull
request #14818 - attributes are no longer be highligted inside of comments
and strings.

Also add some font lock test infrastructure and some tests for attribute
font locking and fix some minor nits.
auto merge of #14984 : thestinger/rust/libc, r=alexcrichton
Revamp TaskBuilder API

This patch consolidates and cleans up the task spawning APIs:

* Removes the problematic `future_result` method from `std::task::TaskBuilder`,
  and adds a `try_future` that both spawns the task and returns a future
  representing its eventual result (or failure).

* Removes the public `opts` field from `TaskBuilder`, instead adding appropriate
  builder methods to configure the task.

* Adds extension traits to libgreen and libnative that add methods to
  `TaskBuilder` for spawning the task as a green or native thread.

Previously, there was no way to benefit from the `TaskBuilder` functionality and
also set the scheduler to spawn within.

With this change, all task spawning scenarios are supported through the
`TaskBuilder` interface.

Closes #3725.

[breaking-change]
Fallout from TaskBuilder changes

This commit brings code downstream of libstd up to date with the new
TaskBuilder API.