except where trait objects are involved.

Part of issue #15349, though I'm leaving it open for trait objects.
Cross borrowing for trait objects remains because it is needed until we
have DST.

This will break code like:

    fn foo(x: &int) { ... }

    let a = box 3i;
    foo(a);

Change this code to:

    fn foo(x: &int) { ... }

    let a = box 3i;
    foo(&*a);

[breaking-change]

for `~str`/`~[]`.

Note that `~self` still remains, since I forgot to add support for
`Box<self>` before the snapshot.

How to update your code:

* Instead of `~EXPR`, you should write `box EXPR`.

* Instead of `~TYPE`, you should write `Box<Type>`.

* Instead of `~PATTERN`, you should write `box PATTERN`.

[breaking-change]

compile-fail tests, run-fail tests, and run-pass tests.

change borrowck error msg: 'declared in outer block' -> 'captured in a closure' (properly this time)

conflict with the new single-line-sugared-inner-doc-comment (`//! ...`).

This reverts commit 7ef825bb.

18s perf regression compiling rustc with opts

This reverts commit 7f6ee0ce.

cc #2540