getopts: cleanup, renames, remove reexports

* Remove public reexports, as a part of #19253
* Rename getopts::Fail_ to getopts::Fail
 * Didn't see a reason for the suffixed '_'
* Removed getopts::FailType
 * Looked like it was only beings used for tests; refactored the tests
   to stop requiring it
* A few other non-breaking trivial refactoring changes

[breaking-change]
impl Str for CowString

This implementation existed on MaybeOwned, but has been lost in the
transition to Cows. Let's put it back.
reword faq to remove reference to indexing strings

Fixes #19344
auto merge of #19345 : steveklabnik/rust/gh19344, r=alexcrichton

Fixes #19344
Fix a simple typo
Fix rustc panic on second compile_input
auto merge of #19401 : MatejLach/rust/guide_are_fix, r=steveklabnik

Fixes a small omission of `are` in the sentence:
`There also a few things you can do with a tuple as a whole, without...`
r @steveklabnik?
auto merge of #19392 : murarth/rust/rustc-compile-twice, r=nick29581

Closes #19371
syntax: Make `asm!` clobbers a proper vector.

Otherwise `--pretty expanded` diverges.
auto merge of #19365 : frewsxcv/rust/getopts-cleanup, r=alexcrichton

* Remove public reexports, as a part of #19253
* Rename getopts::Fail_ to getopts::Fail
 * Didn't see a reason for the suffixed '_'
* Removed getopts::FailType
 * Looked like it was only beings used for tests; refactored the tests
   to stop requiring it
* A few other non-breaking trivial refactoring changes

[breaking-change]
Adjust some error messages to start with a lowercase letter and not finish with a full stop
mk: Use host llvm linkage paths, not target ones

We only build LLVM for the host architecture, not the target architecture, so
this was just a minor typo in the parameters uses.

Closes #19383
Fix the ordering of `unsafe` and `extern` in methods

This breaks code that looks like this:

    trait Foo {
        extern "C" unsafe fn foo();
    }

    impl Foo for Bar {
        extern "C" unsafe fn foo() { ... }
    }

Change such code to look like this:

    trait Foo {
        unsafe extern "C" fn foo();
    }

    impl Foo for Bar {
        unsafe extern "C" fn foo() { ... }
    }

Fixes #19398.

[breaking-change]
trans: Eliminated redundant allocations.
auto merge of #19369 : seanmonstar/rust/cow-str, r=alexcrichton

This implementation existed on MaybeOwned, but has been lost in the
transition to Cows. Let's put it back.

@aturon r?
Fix typo in tests makefile
auto merge of #19411 : lifthrasiir/rust/asm-clobbers-expanded, r=alexcrichton

I.e. we should not prematurely build operand constraints at the expansion time. Otherwise `--pretty expanded` diverges:

```
$ cat t.rs
#![feature(asm)]

pub fn main() { unsafe { asm!("" : : : "hello", "world") }; }

$ rustc t.rs --pretty
#![feature(asm)]

pub fn main() { unsafe { asm!("" : : : "hello" , "world") }; }

$ rustc t.rs --pretty expanded
#![feature(asm)]
#![feature(phase)]
#![no_std]
#![feature(globs)]
#[phase(plugin, link)]
extern crate "std" as std;
#[prelude_import]
use std::prelude::*;

pub fn main() { unsafe { asm!("":  :  : "~{hello},~{world}") }; }
```

(The last code *does* compile, but won't do the expected thing.)
auto merge of #19415 : P1start/rust/error-message-fixes, r=alexcrichton

This is the style followed by most other error messages.
auto merge of #19418 : P1start/rust/unsafe-extern-trait, r=alexcrichton

Fixes #19398.
auto merge of #19425 : frewsxcv/rust/patch-1, r=steveklabnik

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