After a hash mismatch error, emit file-system paths of crates involved.

Fix #13266.

There is a little bit of acrobatics in the definition of `crate_paths`
to avoid calling `clone()` on the dylib/rlib unless we actually are
going to need them.

The other oddity is that I have replaced the `root_ident: Option<&str>`
parameter with a `root: &Option<CratePaths>`, which may surprise one
who was expecting to see something like: `root: Option<&CratePaths>`.
I went with the approach here because I could not come up with code for
the alternative that was acceptable to the borrow checker.
Small change to example to make variable values more sensible.
Removed all instance of `@` in code examples.
rustc: move the check_loop pass earlier.

This pass is purely AST based, and by running it earlier we emit more
useful error messages, e.g. type inference fails in the case of `let r =
break;` with few constraints on `r`, but its more useful to be told that
the `break` is outside a loop (rather than a type error) when it is.

Closes #13292.
Removed cmath and instrinsic wrapper.
Remove references to obsolete `do` keyword

Also add the new `proc` keyword to the documentation.
Added session.fileline_note() method and support infrastucture for it.

Add way to print notes with just file:linenum prefix (preserving
integration with source lookup for e.g. vi and emacs) but don't repeat
the other span info.
Accumulate list of paths for crate hash mismatch.

(i.e. semi-generalized version of prior errorinfo gathering.)

Also revised presentation to put each path on its own line, prefixed
by file:linenum information.
Rough regression test for #13266.

All it checks, unfortunately, is that you actually printed at least
two lines for crateA paths and at least one line for crateB paths.
But that's enough to capture the spirit of the bug, I think.  I did
not bother trying to verify that the paths themselves reflected where
the crates end up.
auto merge of #13284 : pnkfelix/rust/more-fs-info-on-crate-mismatch, r=alexcrichton

Fix #13266.

There is a little bit of acrobatics in the definition of `crate_paths`
to avoid calling `clone()` on the dylib/rlib unless we actually are
going to need them.

The other oddity is that I have replaced the `root_ident: Option<&str>`
parameter with a `root: &Option<CratePaths>`, which may surprise one
who was expecting to see something like: `root: Option<&CratePaths>`.
I went with the approach here because I could not come up with code for
the alternative that was acceptable to the borrow checker.
auto merge of #13329 : ckendell/rust/remmanaged_tutorial, r=brson

Fixes #13287
Completes work started in #13298

Removed all reference to and sample code using managed boxes/pointers.
auto merge of #13330 : huonw/rust/loop-error, r=alexcrichton

rustc: move the check_loop pass earlier.

This pass is purely AST based, and by running it earlier we emit more
useful error messages, e.g. type inference fails in the case of 
`let r = break;` with few constraints on `r`, but it's more useful to be told that
the `break` is outside the loop (rather than a type error) when it is.

Closes #13292.
auto merge of #13331 : pongad/rust/remove-wrapper, r=thestinger

Fixes #12713
auto merge of #13332 : mbrubeck/rust/doc-edit, r=huonw

Also add the new `proc` keyword to the documentation.