`std::ratio` module contains `BigRational` type, but the type is not usable by following reasons.
* `Ratio::new` requires `T: Copy + Num + Ord`, but `BigInt` is not implicitly copyable, because it contains unique vector.
* `BigInt` is not implements `Num`

So, I rewrite `Ratio` as follows.
* `Ratio` requires `T: Clone + Integer + Ord`.
  * `Copy` -> `Clone`: to be able to use `BigRational`
  * `Num` -> `Integer`: It is incorrect that a rational number constructed by two non-integer numbers.
* `BigInt` implements `Num` and `Orderable` which are required by `Integer` bound

`position` and `rposition` belonged to `ImmutableCopyableVector`, but they don't need the value is copyable.

These few commits address a few existing issues:

* #5469 - adding regression tests for `rusti`. This adds unit tests to the `rusti.rc` file (which needed some reorganization of the Makefile, see the first commit message). These are super-simple right now, and sadly can't test the output of the tests. I worked for a bit on making a compiletest version of the rusti tests, but I ended up hitting something which blocked me, although I've forgotten it by this point.
* #5937 - regression test added, and it's fixed
* #5803 - just doesn't appear to happen any more
* #5784 - it's no longer broken, and it no longer spits out warnings about unused variables.

I also did some investigation into #5774, and you may want to read the comment I left on the bug. The gist of the situation is that C++ exceptions across JIT code don't look like they're working, even though they [should be working](https://github.com/mozilla/rust/blob/3aa1122ec25d15a2a73a295f8298ad9c38b09a10/src/rustllvm/RustWrapper.cpp#L387). If anyone has any insight on this, that would be awesome!

* They didn't work before, because the location of the tests caused the
  'sysroot' option to crate lookup to be wrong for finding the correct stage's
  core/std libraries. This moves the compiled tests from the $host/test
  directory into a $host/$stage/test directory. This means that the sysroot will
  be correct and the core/std libraries can actually be found
* The LLVM bindings apparently aren't threadsafe, so we can't run multiple tests
  in parallel.

This closes #5204 and #6421.

This also removes the `vecs_implicitly_copyable` lint (although now reading #6421, this may not be desired?). If we want to leave it in, it at least removes it from the compiler.

fail!() used to require owned strings but can handle static strings
now. Also, it can pass its arguments to fmt!() on its own, no need for
the caller to call fmt!() itself.

fail!() used to require owned strings but can handle static strings
now. Also, it can pass its arguments to fmt!() on its own, no need for
the caller to call fmt!() itself.

This allows creating `Ratio<T>` which `T` is non-implicitly copyable types
such as `BigInt`.

This is part of the numeric trait reform tracked on issue #4819

Also fix up all the fallout elsewhere throughout core. It's really nice being
able to have the prelude.

I'm not quite sure how resolution works with traits, but it seems to me like the public imports at the top-level of the core crate were leaking into the sub-crates, but that could also be working as intended. Regardless, things compile without the re-exports now.

uninit() would result in potentially running a destructor on arbitrary
memory if the Ord implementation throws

This includes 26fa6f8 which fixes #6258

@ILyoan I ported your patches forward and confirmed that they build but you should be aware of this upgrade.

- vec.rs :add 'each2_mut function'
- testsuit : run-pass/vec-each2_mut.rs

uninit() would result in potentially running a destructor on arbitrary
memory if the Ord implementation throws

Also fix up all the fallout elsewhere throughout core. It's really nice being
able to have the prelude.

r? @pcwalton

* Move `SharedMutableState`, `LittleLock`, and `Exclusive` from `core::unstable` to `core::unstable::sync`
* Modernize the `SharedMutableState` interface with methods
* Rename `SharedMutableState` to `UnsafeAtomicRcBox` to match `RcBox`.

r? @graydon