mk: Simplify how prepare.mk, install.mk, and dist.mk deal with stages

The only stage that can be installed from is 2 everywhere but windows,
3 on windows.

Closes #12799
Let travis check docs for stage1
auto merge of #13029 : FlaPer87/rust/master, r=alexcrichton

This should prevent lot of doc errors in Rust's buildbot and it shouldn't take long to run on travis. We could probably limit it to `std` but I preferred to just check all docs in this phase too.

@alexcrichton r?
libstd: Add some methods to `Vec<T>`.
test: Automatically remove all `~[T]` from tests.
test: Make manual changes to deal with the fallout from removal of
`~[T]` in test, libgetopts, compiletest, librustdoc, and libnum.
Rewrite rc::Rc using cell::Cell

Since `Arc` has been using `Atomic`, this closes 12625.

Closes #12625.
auto merge of #12654 : edwardw/rust/rc-arc, r=huonw

Since `Arc` has been using `Atomic`, this closes 12625.

Closes #12625.
Remove outdated and unnecessary std::vec_ng::Vec imports.

(And fix some tests.)
Remove nearly all uses of `~[]` from libtest.

Deny further uses, with explicit allows on a few specific functions.
getopts: remove all uses of `~[]`.

And stop regressions with the lint.
Add #[deny(deprecated_owned_vector)] to several modules.
auto merge of #13056 : huonw/rust/devecing-tests, r=pnkfelix

test: Remove all `~[T]` from tests, libgetopts, compiletest, librustdoc, and libnum

And most from libtest, libflate, and adds `deny(deprecated_owned_vector)`s to the smaller modules with that have zero (or nearly zero) uses of `~[T]`.

Revival of #12837
auto merge of #13024 : brson/rust/issue-12799, r=thestinger

The only stage that can be installed from is 2 everywhere but windows,
3 on windows.

Lightly tested. Not actually tested on Windows, but I did confirm that a *similar* change fixed the problem on Windows.

Closes #12799
Add ty_simd to the compiler to use instead of piggy-backing on ty_struct
Add SIMD syntax, ast and translation support
Improve SIMD typechecking, do translation for arithmetic operators
Implement a somewhat naive equality for SIMD vectors
Feature gate SIMD types
Add indexing support for SIMD vectors