Fix an ICE on a cast from an inferred nil to uint

Fixes #10991.
rustc: Add self/super hint for extern crate resolve errors.
emacs: Don't overwrite font lock for attributes

This addresses the font lock regression introduced by the earlier pull
request #14818 - attributes are no longer be highligted inside of comments
and strings.

Also add some font lock test infrastructure and some tests for attribute
font locking.
emacs: Add shebang to test script
emacs: Remove outdated references to ~ in tests
rustc: reduce redundant resolve errors.
librustc: Don't overwrite vtables when coercing to trait object.
Mark all crates except std as experimental
fix signatures of mmap-related functions from libc
rustdoc: Fix testing indented code blocks

The collapse/unindent passes were run in the wrong order, generating different
markdown for indented tests.
rustdoc: Don't inject `extern crate std`.

No need to duplicate the compiler's work!

Closes #14999
std: Remove dual export of `Show`

Closes #14996
auto merge of #15000 : alexcrichton/rust/fix-rustdoc-tests, r=huonw

Commits have the descriptions.
auto merge of #14990 : tomjakubowski/rust/emacs-fix-attribute-highlight, r=pnkfelix

This addresses the font lock regression introduced by the earlier pull
request #14818 - attributes are no longer be highligted inside of comments
and strings.

Also add some font lock test infrastructure and some tests for attribute
font locking and fix some minor nits.
auto merge of #14984 : thestinger/rust/libc, r=alexcrichton
Bug fixes for flowgraph construction.

1. After recursively processing an ExprWhile, need to pop loop_scopes
   the same way we do for ExprLoop.

2. Proposed fix for flowgraph handling of ExprInlineAsm: we need to
   represent the flow into the subexpressions of an `asm!` block.
NodeIndex should derive `Show`.
Revise dataflow to do a cfg-driven walk.

Fix #6298.

This is instead of the prior approach of emulating cfg traversal
privately by traversing AST in same way).

Of special note, this removes a special case handling of `ExprParen`
that was actually injecting a bug (since it was acting like an
expression like `(*func)()` was consuming `*func` *twice*: once from
`(*func)` and again from `*func`).  nikomatsakis was the first one to
point out that it might suffice to simply have the outer `ExprParen`
do the consumption of the contents (alone).

(This version has been updated to incorporate feedback from Niko's
review of PR 14873.)
middle::cfg code cleanup.

Namely:

 1. Now that cfg mod is used for dataflow, we do not need to turn on
    the `allow(deadcode)` to placate the linter.

 2. remove dead struct defn.
Ensure dataflow of a proc never looks at blocks from closed-over context.

Details: in a program like:
```
type T = proc(int) -> int; /* 4 */

pub fn outer(captured /* pat 16 */: T) -> T {
    (proc(x /* pat 23 */) {
        ((captured /* 29 */).foo((x /* 30 */)) /* 28 */)
    } /* block 27 */ /* 20 */)
} /* block 19 */ /* 12 */
```
the `captured` arg is moved from the outer fn into the inner proc (id=20).

The old dataflow analysis for flowed_move_data_moves, when looking at
the inner proc, would attempt to add a kill bit for `captured` at the
end of its scope; the problem is that it thought the end of the
`captured` arg's scope was the outer fn (id=12), even though at that
point in the analysis, the `captured` arg's scope should now be
restricted to the proc itself (id=20).

This patch fixes handling of upvars so that dataflow of a fn/proc
should never attempts to add a gen or kill bit to any NodeId outside
of the current fn/proc.  It accomplishes this by adding an `LpUpvar`
variant to `borrowck::LoanPath`, so for cases like `captured` above
will carry both their original `var_id`, as before, as well as the
`NodeId` for the closure that is capturing them.

As a drive-by fix to another occurrence of a similar bug that
nikomatsakis pointed out to me earlier, this also fixes
`gather_loans::compute_kill_scope` so that it computes the kill scope
of the `captured` arg to be block 27; that is, the block for the proc
itself (id=20).

(This is an updated version that generalizes the new loan path variant
to cover all upvars, and thus renamed the variant from `LpCopiedUpvar`
to just `LpUpvar`.)