Replace StrAllocating.into_owned() with .into_string()

We already have into_string(), but it was implemented in terms of
into_owned(). Flip it around and deprecate into_owned().

Remove a few spurious calls to .into_owned() that existed in libregex
and librustdoc.
remove /build from .gitignore since there is build/
Revert erroneous fix to tutorial
syntax: Fix span on illegal ABI errors

Fixes #8537
Fixes #14499
Change to_owned() to to_string().
Make Arc::make_unique check weak refs; add make_unique to Rc

This patch makes `Arc::make_unique` examine the number of weak
references as well as strong references, which is required for safety.

It also adds a `make_unique` method to the `Rc` type for consistency.

Closes #14521.
std: Recreate a `rand` module

This commit shuffles around some of the `rand` code, along with some
reorganization. The new state of the world is as follows:

* The librand crate now only depends on libcore. This interface is experimental.
* The standard library has a new module, `std::rand`. This interface will
  eventually become stable.

Unfortunately, this entailed more of a breaking change than just shuffling some
names around. The following breaking changes were made to the rand library:

* Rng::gen_vec() was removed. This has been replaced with Rng::gen_iter() which
  will return an infinite stream of random values. Previous behavior can be
  regained with `rng.gen_iter().take(n).collect()`

* Rng::gen_ascii_str() was removed. This has been replaced with
  Rng::gen_ascii_chars() which will return an infinite stream of random ascii
  characters. Similarly to gen_iter(), previous behavior can be emulated with
  `rng.gen_ascii_chars().take(n).collect()`

* {IsaacRng, Isaac64Rng, XorShiftRng}::new() have all been removed. These all
  relied on being able to use an OSRng for seeding, but this is no longer
  available in librand (where these types are defined). To retain the same
  functionality, these types now implement the `Rand` trait so they can be
  generated with a random seed from another random number generator. This allows
  the stdlib to use an OSRng to create seeded instances of these RNGs.

* Rand implementations for `Box<T>` and `@T` were removed. These seemed to be
  pretty rare in the codebase, and it allows for librand to not depend on
  liballoc.  Additionally, other pointer types like Rc<T> and Arc<T> were not
  supported.  If this is undesirable, librand can depend on liballoc and regain
  these implementations.

* The WeightedChoice structure is no longer built with a `Vec<Weighted<T>>`,
  but rather a `&mut [Weighted<T>]`. This means that the WeightedChoice
  structure now has a lifetime associated with it.

* The `sample` method on `Rng` has been moved to a top-level function in the
  `rand` module due to its dependence on `Vec`.

cc #13851

[breaking-change]
auto merge of #14427 : alexcrichton/rust/librand, r=huonw

This commit shuffles around some of the `rand` code, along with some
reorganization. The new state of the world is as follows:

* The librand crate now only depends on libcore. This interface is experimental.
* The standard library has a new module, `std::rand`. This interface will
  eventually become stable.

Unfortunately, this entailed more of a breaking change than just shuffling some
names around. The following breaking changes were made to the rand library:

* Rng::gen_vec() was removed. This has been replaced with Rng::gen_iter() which
  will return an infinite stream of random values. Previous behavior can be
  regained with `rng.gen_iter().take(n).collect()`

* Rng::gen_ascii_str() was removed. This has been replaced with
  Rng::gen_ascii_chars() which will return an infinite stream of random ascii
  characters. Similarly to gen_iter(), previous behavior can be emulated with
  `rng.gen_ascii_chars().take(n).collect()`

* {IsaacRng, Isaac64Rng, XorShiftRng}::new() have all been removed. These all
  relied on being able to use an OSRng for seeding, but this is no longer
  available in librand (where these types are defined). To retain the same
  functionality, these types now implement the `Rand` trait so they can be
  generated with a random seed from another random number generator. This allows
  the stdlib to use an OSRng to create seeded instances of these RNGs.

* Rand implementations for `Box<T>` and `@T` were removed. These seemed to be
  pretty rare in the codebase, and it allows for libcore to not depend on
  liballoc.  Additionally, other pointer types like Rc<T> and Arc<T> were not
  supported.  If this is undesirable, librand can depend on liballoc and regain
  these implementations.

* The WeightedChoice structure is no longer built with a `Vec<Weighted<T>>`,
   but rather a `&mut [Weighted<T>]`. This means that the WeightedChoice
   structure now has a lifetime associated with it.

cc #13851

[breaking-change]
auto merge of #14510 : kballard/rust/rename_strallocating_into_owned, r=alexcrichton

We already have into_string(), but it was implemented in terms of
into_owned(). Flip it around and deprecate into_owned().

Remove a few spurious calls to .into_owned() that existed in libregex
and librustdoc.
auto merge of #14512 : Heather/rust/patch-1, r=alexcrichton
Implement Show for Bitv{,Set}

Closes #14531
Rename OSRng to OsRng

According to Rust's style guide acronyms in type names should be
CamelCase.

[breaking-change]
Fix the handling of assignments to owning pointer paths in check_loans

Make check_for_assignment_to_restricted_or_frozen_location treat
mutation through an owning pointer the same way it treats mutation
through an &mut pointer, where mutability must be inherited from the
base path.

I also included GC pointers in this check, as that is what the
corresponding code in gather_loans/restrictions.rs does, but I don't
think there is a way to test this with the current language.

Fixes #14498.
auto merge of #14511 : Sawyer47/rust/osrng-rename, r=alexcrichton

According to Rust's style guide acronyms in type names should be
CamelCase.

[breaking-change]
auto merge of #14514 : Randati/rust/patch-1, r=huonw
auto merge of #14517 : lucy/rust/issue-14499, r=alexcrichton

Fixes #8537
Fixes #14499 (duplicate of #8537)

Old:
```rust
test.rs:2 	pub extern "xxxxx" fn add(x: int, y: int) -> int {
          	                   ^~
```

New:
```rust
test.rs:2 	pub extern "xxxxx" fn add(x: int, y: int) -> int {
          	           ^~~~~~~
```
auto merge of #14522 : aturon/rust/make_unique, r=alexcrichton,alexcrichton,me

This patch makes `Arc::make_unique` examine the number of weak
references as well as strong references, which is required for safety.

It also adds a `make_unique` method to the `Rc` type for consistency.

Closes #14521.
auto merge of #14524 : ahmedcharles/rust/to_string, r=alexcrichton
auto merge of #14535 : sfackler/rust/bitv-show, r=alexcrichton

Closes #14531
rustc: Add lint for snake_case functions & methods.