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.
Mark LineIterator as public so its docs get generated.
extra: Ignore time tests on android correctly
libstd: Added more #[inline] annotations and replaced uses of `libc::abort` with the intrinsic.
auto merge of #11557 : brson/rust/anotherandroidfix, r=thestinger
Fix formatting in rust-guide document.
auto merge of #11556 : am0d/rust/docs, r=huonw
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.
auto merge of #11523 : alexcrichton/rust/stage3, r=brson

This should go back to the old behavior while preserving the snapshot ease.
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.