Coercions will now attempt to autoderef as needed before reborrowing.
This includes overloaded `Deref`, e.g. `&Rc<T>` coerces to `&T`, and
`DerefMut`, e.g. `&mut Vec<T>` coerces to `&mut [T]` (in addition to `&[T]`).
Closes #21432.

trans: When coercing to `Box<Trait>` or `Box<[T]>`, leave datum in it's original L-/R-value state.

This fixes a subtle issue where temporaries were being allocated (but not necessarily initialized) to the (parent) terminating scope of a match expression; in particular, the code to zero out the temporary emitted by `datum.store_to` is only attached to the particular match-arm for that temporary, but when going down other arms of the match expression, the temporary may falsely appear to have been initialized, depending on what the stack held at that location, and thus may have its destructor erroneously run at the end of the terminating scope.

FIx #20055.

(There may be a latent bug still remaining in `fn into_fat_ptr`, but I am so annoyed by the test/run-pass/coerce_match.rs failures that I want to land this now.)

It was considered to be impossible but actually it can
happen for nested closures. Also, because there must
be nested closures when this happens, we can use more
targeted help message.

Closes #21390
Closes #21600

Note: Do not merge until we get a newer snapshot that includes #21374

There was some type inference fallout (see 4th commit) because type inference with `a..b` is not as good as with `range(a, b)` (see #21672).

r? @alexcrichton 

sed -i 's/in range(\([^,]*\), *\([^()]*\))/in \1\.\.\2/g' **/*.rs

sed -i 's/ range(\([^,]*\), *\([^()]*\))\./ (\1\.\.\2)\./g' **/*.rs

Should clear our backlog of rollups from the queue

Replaces `slice_*` method calls with slicing syntax, and removes `as_slice()` calls that are redundant due to `Deref`.

Do not propagate the region requirements on the projected type to the input types it is being projected from.

Fixes #21520.

r? @aturon 

Rollup merge of 21651 - nelsonjchen:add--webkit-overflow-scrolling-touch-to-book-css, r=alexcrichton

`_wrmdir` is literally just a wrapper around `RemoveDirectoryW`, so let's just use `RemoveDirectoryW`.
r? @alexcrichton 

This should work now.

Conflicts:
	src/libcollections/slice.rs
	src/libcore/nonzero.rs
	src/libcore/ops.rs

New email address, stylization of name.

Fixes https://github.com/rust-lang/rust/issues/20871

r? @aturon (at least until we decide definitively if this is a good idea)