add an experimental tag for Gc<T> due to cycles

This type isn't yet very useful since it only pretends cycles won't be
a problem. Anyone using it should be made aware that they're going to
leak.
Flag failure functions as inline(never)

The failure functions are generic, meaning they're candidates for getting
inlined across crates. This has been happening, leading to monstrosities like
that found in #11549. I have verified that the codegen is *much* better now that
we're not inlining the failure path (the slow path).
libstd: Added more #[inline] annotations and replaced uses of `libc::abort` with the intrinsic.
Fix formatting in rust-guide document.
register snapshots
remove the concept of managed-unique from libstd

Closes #11545
auto merge of #11561 : eddyb/rust/moar-inlines, r=pcwalton
auto merge of #11564 : am0d/rust/dox, r=huonw

Needs a line break here for readability.
Add a configure to disable libstd version injection

We'll use this when building snapshots so we can upgrade freely, but all
compilers will inject a version by default.
Revert "show options for -W help and -W". Fixes #11458.

This reverts commit 1009c21ad7b1db366a5c600946652cc490598ec1.
auto merge of #11523 : alexcrichton/rust/stage3, r=brson

This should go back to the old behavior while preserving the snapshot ease.
Use the least significant beat to determine if int/uint is even
auto merge of #11543 : thestinger/rust/gc, r=cmr

This type isn't yet very useful since it only pretends cycles won't be
a problem. Anyone using it should be made aware that they're going to
leak.
Allow more "error" values in try_recv()

This should allow callers to know whether the channel was empty or disconnected
without having to block.

Closes #11087
auto merge of #11112 : alexcrichton/rust/issue-11087, r=brson

This should allow callers to know whether the channel was empty or disconnected
without having to block.

Closes #11087
auto merge of #11550 : alexcrichton/rust/noinline, r=thestinger

The failure functions are generic, meaning they're candidates for getting
inlined across crates. This has been happening, leading to monstrosities like
that found in #11549. I have verified that the codegen is *much* better now that
we're not inlining the failure path (the slow path).
auto merge of #11568 : FlaPer87/rust/even, r=alexcrichton

This implementation should be a bit more optimal than calling `self.is_multiple_of(&2)`
auto merge of #11565 : mozilla/rust/snapshot, r=huonw
auto merge of #11574 : neeee/rust/master, r=alexcrichton

Reverted according to https://github.com/mozilla/rust/issues/11458#issuecomment-32269477. Fixes #11458.
doc: Boxes diagram shows enum value inside box.