De-spanned<T> and renamed ast::field (now ast::Field)
auto merge of #7903 : michaelwoerister/rust/end_of_spanned, r=jdm

Continuation of https://github.com/mozilla/rust/pull/7826.

AST spanned<T> refactoring, AST type renamings:

`crate => Crate`
`local => Local`
`blk => Block`
`crate_num => CrateNum`
`crate_cfg => CrateConfig`
`field => Field`

Also, Crate, Field and Local are not wrapped in spanned<T> anymore.
dlist: Fix .peek_next() w.r.t double ended iterators

.peek_next() needs to check the element counter just like the .next()
and .next_back() iterators do.

Also clarify .insert_next() doc w.r.t double ended iteration.
auto merge of #7940 : cmr/rust/comments, r=pnkfelix
auto merge of #7942 : Dretch/rust/os-listdir-path-no-squiggle, r=brson
std: add RtioTimer and UvTimer impl atop rt::uv
std: add rt::io::Timer
std: minor timer cleanup based on feedback
std: make check appeasement
auto merge of #7943 : Dretch/rust/vec-slice-from-to, r=huonw
extra: Remove uv, net, timer code

This will all be reimplemented in the new runtime.
extra: Add url module

Used to be under extra::net, which no longer exists
std: Remove weak_task API. Unused
std::rt: Stop using unstable::global in change_dir_locked
std: Move change_dir_locked to unstable. #7870
std: Remove unstable::global. Unused
std: Remove at_exit API. Unused
Change libaux directory to fix aux crate tests on Windows
std: fix for blocked task resume
auto merge of #7883 : brson/rust/rm-std-net, r=graydon

This removes all the code from libextra that depends on libuv. After that it removes three runtime features that existed to support the global uv loop: weak tasks, runtime-global variables, and at_exit handlers.

The networking code doesn't have many users besides servo, so shouldn't have much fallout. The timer code though is useful and will probably break out-of-tree code until the new scheduler lands, but I expect that to be soon.

It also incidentally moves `os::change_dir_locked` to `std::unstable`. This is a function used by test cases to avoid cwd races and in my opinion shouldn't be public (#7870).

Closes #7251 and #7870