Also remove a period on a different help line for consistency

This seems to have been undocumented. Mention this where the name is set
(Builder::name) and where the panic could happen (Builder::spawn).

Thread::new is private and I think the builder is the only user where
this matters. A short comment was added to "document" Thread::new too.

After the following conversation in #rust-lang:
```
[14:43:50] <Ixrec> TIL the implementation of from_utf_unchecked is literally just "mem::transmute(x)"
[14:43:59] <Ixrec> no wonder people keep saying transmute is overpowered
[15:15:30] <eddyb> Ixrec: it should be a pointer cast lol
[15:15:46] <eddyb> unless it doesn't let you
[16:50:34] <Ixrec> https://play.rust-lang.org/?gist=d1e6b629ad9ec1baf64ce261c63845e6&version=stable seems like it does let me
[16:52:35] <eddyb> Ixrec: yeah that's the preferred impl
[16:52:46] <eddyb> Ixrec: it just wasn't in 1.0
[16:52:50] <eddyb> IIRC
[16:53:00] <eddyb> (something something fat pointers)
```
Since I already wrote half of the preferred impls in the playground, might as well make an actual PR.

Part of rust-lang#44600.

These Region values end up in crate metadata so they should not use NodeId.

This makes sure that we don't introduce strange cases where we have
nodes outside the query system that could break red/green tracking
and it will allow to keep red/green neatly encapsulated within the
DepGraph implementation.

- Don't hash traits in scope as part of HIR hashing any more.
- Some queries returned DefIndexes from other crates.
- Provide a generic way of stably hashing maps (not used everywhere yet).

…n't have to be hashed in downstream crates.

…t maps.

… lazily.

…s2, r=nikomatsakis

incr.comp.: Compute fingerprint for all query results.

This PR enables query result fingerprinting in incremental mode. This is an essential piece of infrastructure for red/green tracking. We don't do anything with the fingerprints yet but merging the infrastructure should protect it from bit-rotting and will make it easier to start measuring its performance impact (and thus let us determine if we should switch to a faster hashing algorithm rather sooner than later).

Note, this PR also includes the changes from rust-lang#43887 which I'm therefore closing. No need to re-review the first commit though.

r? @nikomatsakis

Add Cow<str> -> Box<Error> impls.

Considering how impls exist for `String` and `&str`, it makes sense to also add an impl for `Cow<str>` as well.

This would allow converting `String::from_utf8_lossy` directly into a `Box<Error>` or `io::Error` without having to add an extra `into_ownd()`.

More `align_offset` things

cc rust-lang#44488

Add proper help line for `-C inline threshold`

Looks like someone accidentally some words when adding this.

This also remove a period on a different help line for consistency, as no options have a period.

Stabilized vec_splice and modified splice tracking issue

This stabilizes the vec_splice (Vec part of splice RFC)
Fixes rust-lang#32310.

… r=steveklabnik

Document thread builder panics for nul bytes in thread names

This seems to have been undocumented. Mention this where the name is set
(Builder::name) and where the panic could happen (Builder::spawn).

Thread::new is private and I think the builder is the only user where
this matters. A short comment was added to "document" Thread::new too.

Replace str's transmute() calls with pointer casts

After the following conversation in #rust-lang:
```
[14:43:50] <Ixrec> TIL the implementation of from_utf_unchecked is literally just "mem::transmute(x)"
[14:43:59] <Ixrec> no wonder people keep saying transmute is overpowered
[15:15:30] <eddyb> Ixrec: it should be a pointer cast lol
[15:15:46] <eddyb> unless it doesn't let you
[16:50:34] <Ixrec> https://play.rust-lang.org/?gist=d1e6b629ad9ec1baf64ce261c63845e6&version=stable seems like it does let me
[16:52:35] <eddyb> Ixrec: yeah that's the preferred impl
[16:52:46] <eddyb> Ixrec: it just wasn't in 1.0
[16:52:50] <eddyb> IIRC
[16:53:00] <eddyb> (something something fat pointers)
```
Since I already wrote half of the preferred impls in the playground, might as well make an actual PR.

…isdreavus

Add more links and put the link character to the left

r? @QuietMisdreavus

And of course, a few screenshots:

<img width="1440" alt="screen shot 2017-09-17 at 22 08 46" src="https://user-images.githubusercontent.com/3050060/30524496-44a50208-9bf5-11e7-942e-a3707ba125c3.png">
<img width="1440" alt="screen shot 2017-09-17 at 22 09 47" src="https://user-images.githubusercontent.com/3050060/30524502-49068dbc-9bf5-11e7-8e59-ec38664e0e0f.png">
<img width="1440" alt="screen shot 2017-09-17 at 22 10 56" src="https://user-images.githubusercontent.com/3050060/30524503-491c8c34-9bf5-11e7-9ce5-f1bd5ef8600b.png">

…eveklabnik

Add Example of `IntoIterator` as Trait Bound to Docs

Part of rust-lang#44600.

…labnik

Fix run button

r? @QuietMisdreavus

Before:

![before](https://user-images.githubusercontent.com/3050060/30538927-612c6a44-9c70-11e7-9ca2-f3860d880b95.png)

After:

![after](https://user-images.githubusercontent.com/3050060/30538929-6416ea0e-9c70-11e7-990a-7e4fbf5d7319.png)

Quite urgent.