This commit stabilizes `std::borrow`, making the following modifications
to catch up the API with language changes:

* It renames `BorrowFrom` to `Borrow`, as was originally intended (but
  blocked for technical reasons), and reorders the parameters
  accordingly.

* It moves the type parameter of `ToOwned` to an associated type. This
  is somewhat less flexible, in that each borrowed type must have a
  unique owned type, but leads to a significant simplification for
  `Cow`. Flexibility can be regained by using newtyped slices, which is
  advisable for other reasons anyway.

* It removes the owned type parameter from `Cow`, making the type much
  less verbose.

* Deprecates the `is_owned` and `is_borrowed` predicates in favor of
  direct matching.

The above API changes are relatively minor; the basic functionality
remains the same, and essentially the whole module is now marked
`#[stable]`.

[breaking-change]

that it produces "outlives" relations for associated types. Add
several tests relating to #22246.

parameter environments so that it can be used elsewhere.

`no_late_bound_regions().unwrap()`, which allows us to write code that
doesn't necessarily *fail* when there are higher-ranked trait bounds.

 One windows bot failed spuriously.

Conflicts:
	src/libstd/sync/task_pool.rs
	src/libstd/thread.rs
	src/libtest/lib.rs
	src/test/bench/shootout-reverse-complement.rs
	src/test/bench/shootout-spectralnorm.rs

Requested by Niko in #22200 (and is good to have anyway)

Conflicts:
	src/test/bench/rt-messaging-ping-pong.rs
	src/test/bench/rt-parfib.rs
	src/test/bench/task-perf-spawnalot.rs

An "immutable reference-counted pointer" is confusing, one might think that the `Rc` itself is immutable which isn't the case.
cf. http://www.reddit.com/r/rust/comments/2w75wr/how_do_i_read_immutable_vector_inside_a_spawned/coo6mm2

Conflicts:
	src/rustbook/main.rs

FIxes #22361

Noticed in #22429

Implement `Vec::from_elem` by making the `vec![element; len]` macro more powerful (see rust-lang/rfcs#832).

Closes #22414

r? @Gankro

Now that the necessary associated types exist for the `IntoIterator` trait this
commit stabilizes the trait as-is as well as all existing implementations.

The `connect_error` test check if connecting to "0.0.0.0:1" works (it
shouldn't). And in case of error, the test expects a `ConnectionRefused`
error.

Under OpenBSD, trying to connect to "0.0.0.0" isn't a `ConnectionRefused`:
it is an `InvalidInput` error.

The patch allow the error to be `ConnectionRefused` or `InvalidInput`.

Another possibility is to check connecting to "127.0.0.1:1" and expects only `ConnectionRefused` error.

Fixes the crash blocking #21886.

Fixes #19315

r? @aturon

Requested by Niko in #22200 (and is good to have anyway)

This commit exposes the `is_sep` function and `MAIN_SEP` constant, as
well as Windows path prefixes. The path prefix enum is safely exposed on
all platforms, but it only yielded as a component for Windows.

Exposing the prefix enum as part of prefix components involved changing
the type from `OsStr` to the `Prefix` enum, which is a:

[breaking-change]

This aligns json target specification to match terminology used elsewhere in the code base.

[breaking-change] for custom target json users. Change all appearances of target-word-size
to target-pointer-width.

Closes #21859.

* Move the type parameter on the `AsciiExt` trait to an associated type named
  `Owned`.
* Move `ascii::escape_default` to using an iterator.

This is a breaking change due to the removal of the type parameter on the
`AsciiExt` trait as well as the modifications to the `escape_default` function
to returning an iterator. Manual implementations of `AsciiExt` (or `AsciiExt`
bounds) should be adjusted to remove the type parameter and using the new
`escape_default` should be relatively straightforward.

[breaking-change]

This commit makes several changes to `std::thread` in preparation for
final stabilization:

* It removes the ability to handle panics from `scoped` children; see
  #20807 for discussion

* It adds a `JoinHandle` structure, now returned from `spawn`, which
  makes it possible to join on children that do not share data from
  their parent's stack. The child is automatically detached when the
  handle is dropped, and the handle cannot be copied due to Posix
  semantics.

* It moves all static methods from `std::thread::Thread` to free
  functions in `std::thread`. This was done in part because, due to the
  above changes, there are effectively no direct `Thread` constructors,
  and the static methods have tended to feel a bit awkward.

* Adds an `io::Result` around the `Builder` methods `scoped` and
  `spawn`, making it possible to handle OS errors when creating
  threads. The convenience free functions entail an unwrap.

* Stabilizes the entire module. Despite the fact that the API is
  changing somewhat here, this is part of a long period of baking and
  the changes are addressing all known issues prior to alpha2. If
  absolutely necessary, further breaking changes can be made prior to beta.

Closes #20807

[breaking-change]

This commit renames the features for the `std::old_io` and `std::old_path`
modules to `old_io` and `old_path` to help facilitate migration to the new APIs.

This is a breaking change as crates which mention the old feature names now need
to be renamed to use the new feature names.

[breaking-change]

This commit performs a stabilization pass over the `std::ascii` module taking
the following actions:

* the module name is now stable
* `AsciiExt` is now stable after moving its type parameter to an `Owned`
  associated type
* `AsciiExt::is_ascii` is now stable
* `AsciiExt::to_ascii_uppercase` is now stable
* `AsciiExt::to_ascii_lowercase` is now stable
* `AsciiExt::eq_ignore_ascii_case` is now stable
* `AsciiExt::make_ascii_uppercase` is added to possibly replace
  `OwnedAsciiExt::into_ascii_uppercase` (similarly for lowercase variants).
* `escape_default` now returns an iterator and is stable
* `EscapeDefault` is now stable

Trait implementations are now also marked stable.

Primarily it is still unstable to *implement* the `AsciiExt` trait due to it
containing some unstable methods.

[breaking-change]

Previously an implementation of a stable trait allows implementations of
unstable methods. This updates the stability pass to ensure that all items of an
impl block of a trait are indeed stable on the trait itself.

The lifetime was previously, incorrectly unconstrained.