std: Bring back half of Add on String

This adds an implementation of Add for String where the rhs is <S: Str>. The
other half of adding strings is where the lhs is <S: Str>, but coherence and
the libcore separation currently prevent that.
librustc: Remove the fallback to `int` from typechecking.

This breaks a fair amount of code. The typical patterns are:

* `for _ in range(0, 10)`: change to `for _ in range(0u, 10)`;

* `println!("{}", 3)`: change to `println!("{}", 3i)`;

* `[1, 2, 3].len()`: change to `[1i, 2, 3].len()`.

RFC #30. Closes #6023.

[breaking-change]
Add more description to c_str::unwrap().

It's unclear what you are supposed to do with this memory.
Let's make that more clear.
Add tests for #12470 and #14285

The #14869 removed `TraitStore` from `ty_trait` and represented trait
reference as regular `ty_rptr`. An old bug of the missing constraint
upon lifetime parameter of trait reference then is fixed as a side
effect. Adds tests for affected bugs and closes them.

Closes #12470.
Closes #14285.
Remove the cheat sheet.

Rust by Example is far better.

Fixes #14380.
rustc: Always include the morestack library

It was previously assumed that the object file generated by LLVM would always
require the __morestack function, but that assumption appears to be incorrect,
as outlined in #15108. This commit forcibly tells the linker to include the
entire archive, regardless of whether it's currently necessary or not.

Closes #15108
Improve ambiguous pronoun.

Fixes #14806
Fix #15129

Add support for unit literals to const_eval.
Add the Guide, add warning to tutorial.

In line with what @brson, @cmr, @nikomatsakis and I discussed this morning, my
redux of the tutorial will be implemented as the Guide. This way, I can work in
small iterations, rather than dropping a huge PR, which is hard to review.  In
addition, the community can observe my work as I'm doing it.

This adds a note in line with [this comment][reddit] that clarifies the state
of the tutorial, and the community's involvement with it.

[reddit]: http://www.reddit.com/r/rust/comments/28bew8/rusts_documentation_is_about_to_drastically/ci9c98k
added xfailed tests for two other flavors of var hygiene
added xfailed test for issue 9737
core: Add stability attributes to Clone

The following are tagged 'unstable'

- core::clone
- Clone
- Clone::clone
- impl Clone for Arc
- impl Clone for arc::Weak
- impl Clone for Rc
- impl Clone for rc::Weak
- impl Clone for Vec
- impl Clone for Cell
- impl Clone for RefCell
- impl Clone for small tuples

The following are tagged 'experimental'

- Clone::clone_from - may not provide enough utility
- impls for various extern "Rust" fns - may not handle lifetimes correctly

See https://github.com/rust-lang/rust/wiki/Meeting-API-review-2014-06-23#clone
core: Remove bool::to_bit

This is an unused one-liner.
Move core::bool tests to run-pass

These are closer to language tests than library.
std: Add stability attributes to primitive numeric modules

The following are unstable:

- core::int, i8, i16, i32, i64
- core::uint, u8, u16, u32, u64
- core::int::{BITS, BYTES, MIN, MAX}, etc.
- std::int, i8, i16, i32, i64
- std::uint, u8, u16, u32, u64

The following are experimental:
- std::from_str::FromStr and impls - may need to return Result instead of Option
- std::int::parse_bytes, etc. - ditto
- std::num::FromStrRadix and impls - ditto
- std::num::from_str_radix - ditto

The following are deprecated:
- std::num::ToStrRadix and imples - Wrapper around fmt::radix. Wrong name (Str vs String)

See https://github.com/rust-lang/rust/wiki/Meeting-API-review-2014-06-23#uint
Fix grammar in tutorial

"as this document" should be "than this document"
Remove few FIXMEs

This commit removes FIXMEs of few closed issues.

Closes #13992
Avoid unnecessary temporary on assignments

We only need the temporary when the type needs to be dropped, for other
types, we can use trans_into to directly place the value into the
destination.
Use macros to implement syntax::ext::quote::ToSource

This code deserves a bigger refactor, but here's a local improvement.
Allow splicing more things in quotes