Upgrade libuv
auto merge of #6456 : brson/rust/libuv, r=brson

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.
auto merge of #6461 : thestinger/rust/fix_priority_queue, r=pcwalton

uninit() would result in potentially running a destructor on arbitrary
memory if the Ord implementation throws
auto merge of #6441 : alexcrichton/rust/issue-5531, r=luqmana

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.
auto merge of #6463 : bjz/rust/numeric-traits, r=thestinger

This is part of the numeric trait reform tracked on issue #4819
Move `position` and `rposition` methods to `ImmutableVector` trait
libstd: impl Num for BigUint/BigInt
Update .gitignore
libstd: impl `Orderable` for `BigUint`/`BigInt`
libstd: `Rational` requires `Integer` as type bounds instead of `Num`
libstd: `Ratio` requires `Clone` instead of `Copy`

This allows creating `Ratio<T>` which `T` is non-implicitly copyable types
such as `BigInt`.
libstd: Add tests for BigRational
Replace shared/unique by managed/owned in the tutorial
Issue #5967: Make rvalues mutable
Add explanatory comment to is_rvalue_or_immutable()
Use static string with fail!() and remove fail!(fmt!())

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.
Fix cosmetics for fail!() calls
auto merge of #6357 : dotdash/rust/fixfmt, r=bstrie

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.
rustpkg: Remove #[allow(vecs_implicitly_copyable)]
compiletest: Remove #[allow(vecs_implicitly_copyable)]