Update documentation for from_raw_parts

Fixes #19269.
collections: dramatically speed up Vec::reserve with magic

Somehow llvm is able to optimize this version of Vec::reserve
into dramatically faster than the old version. In micro-benchmarks
this was 2-10 times faster. It also shaved 14 minutes off of
rust's compile times.

Closes #19281.
Add doctests for keys() and values() of the BTreeMap collection.

Update keys() and values() for BTreeMap based on @Gankro's comments.

Assign keys and values to variables before doing assertion.
Allow message specification for should_fail

The test harness will make sure that the panic message contains the
specified string. This is useful to help make `#[should_fail]` tests a
bit less brittle by decreasing the chance that the test isn't
"accidentally" passing due to a panic occurring earlier than expected.
The behavior is in some ways similar to JUnit's `expected` feature:
`@Test(expected=NullPointerException.class)`.

Without the message assertion, this test would pass even though it's not
actually reaching the intended part of the code:
```rust
 #[test]
 #[should_fail(message = "out of bounds")]
fn test_oob_array_access() {
    let idx: uint = from_str("13o").unwrap(); // oops, this will panic
    [1i32, 2, 3][idx];
}
```
Change from message to expected
Mention expected in testing docs
auto merge of #19555 : jbranchaud/rust/add-doctests-for-key-values-of-btreemap, r=Gankro
core: remove the dead function fmt::argumentstr.
core: make the public fmt API completely safe.
test: adjust pretty/issue-4264 for formatting changes.
auto merge of #19506 : eddyb/rust/fmt-polish, r=alexcrichton
auto merge of #19560 : sfackler/rust/should-fail-reason, r=alexcrichton

The test harness will make sure that the panic message contains the
specified string. This is useful to help make `#[should_fail]` tests a
bit less brittle by decreasing the chance that the test isn't
"accidentally" passing due to a panic occurring earlier than expected.
The behavior is in some ways similar to JUnit's `expected` feature:
`@Test(expected=NullPointerException.class)`.

Without the message assertion, this test would pass even though it's not
actually reaching the intended part of the code:
```rust
#[test]
#[should_fail(message = "out of bounds")]
fn test_oob_array_access() {
    let idx: uint = from_str("13o").unwrap(); // oops, this will panic
    [1i32, 2, 3][idx];
}
```
auto merge of #19306 : steveklabnik/rust/gh19269, r=nikomatsakis,brson

Fixes #19269.

/cc @thestinger @mahkoh @mitsuhiko
auto merge of #19574 : erickt/rust/vec-reserve, r=alexcrichton

(I don't understand why this works, and so I don't quite trust this yet. I'm pushing it up to see if anyone else can replicate this performance increase)

Somehow llvm is able to optimize this version of Vec::reserve into dramatically faster than the old version. In micro-benchmarks this was 2-10 times faster. It also reduce my Rust compile time from 41 minutes to 27 minutes.

Closes #19281.
Link regions in `ref` bindings from fn arguments.
auto merge of #19456 : nikomatsakis/rust/reborrow-closure-arg, r=pnkfelix

Otherwise region inference can fail when closure arguments include `ref` bindings. Test case included in the PR.