rustc: Support stability attributes on crates

This commit adds support for linting `extern crate` statements for stability
attributes attached to the crate itself. This is likely to be the mechanism used
to deny access to experimental crates that are part of the standard
distribution.

cc #18585
Use operator sugar in the expansion of `#[deriving(PartialEq)]`
Fix fallout of changing the expansion of `#[deriving(PartialEq)]`
DSTify PartialEq, PartialOrd, Eq, Ord
Fix fallout of DSTifying PartialEq, PartialOrd, Eq, Ord
DSTify Box<T> implementation of PartialEq, PartialOrd, Eq, Ord
Add test for the first half of issue #15689

cc #15689
Fix tests
Add blanket impls to allow the various `Fn` traits to be interconverted.

Fixes #18387.
Reverse order of lookup
Partial fix for #17901: Be less conservative around unbound type
variables in the intracrate case. This requires a deeper distinction
between inter- and intra-crate so as to keep coherence working.

I suspect the best fix is to generalize the recursion check that
exists today, but this requires a bit more refactoring to achieve.

(In other words, where today it says OK for an exact match, we'd want
to not detect exact matches but rather skolemize each trait-reference
fresh and return AMBIG -- but that requires us to make builtin bounds
work shallowly like everything else and move the cycle detection into
the fulfillment context.)
Correct tests that were supposed to fail but now pass due to the fn trait hierarchy.
auto merge of #18388 : nikomatsakis/rust/fn-trait-hierarchy, r=acrichto

Add blanket impls to allow the various `Fn` traits to be interconverted.

Fixes #18387.
auto merge of #18467 : japaric/rust/eq, r=alexcrichton

`eq`, `ne`, `cmp`, etc methods now require one less level of indirection when dealing with `&str`/`&[T]`

``` rust
"foo".ne(&"bar") -> "foo".ne("bar")
slice.cmp(&another_slice) -> slice.cmp(another_slice)
// slice and another_slice have type `&[T]`
```

[breaking-change]
auto merge of #18608 : alexcrichton/rust/lint-some-crates, r=aturon

This commit adds support for linting `extern crate` statements for stability
attributes attached to the crate itself. This is likely to be the mechanism used
to deny access to experimental crates that are part of the standard
distribution.

cc #18585 

r? @aturon