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.
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]
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?
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.)