libstd: Refactor Duration.

This changes the internal representation of `Duration` from

    days: i32,
    secs: i32,
    nanos: u32

to

    secs: i64,
    nanos: i32

This resolves #16466. Some methods now take `i64` instead of `i32` due
to the increased range. Some methods, like `num_milliseconds`, now
return an `Option<i64>` instead of `i64`, because the range of
`Duration` is now larger than e.g. 2^63 milliseconds.
libstd: Limit Duration range to i64 milliseconds.

This enables `num_milliseconds` to return an `i64` again instead of
`Option<i64>`, because it is guaranteed not to overflow.

The Duration range is now rougly 300e6 years (positive and negative),
whereas it was 300e9 years previously. To put these numbers in
perspective, 300e9 years is about 21 times the age of the universe
(according to Wolfram|Alpha). 300e6 years is about 1/15 of the age of
the earth (according to Wolfram|Alpha).
librustc: Don't ICE with type when name only contain underscores.
extern crate foobar as foo;

Implements remaining part of RFC #47.
Addresses issue #16461.

Removed link_attrs from rust.md, they don't appear to be supported by
the parser.

Changed all the tests to use the new extern crate syntax

Change pretty printer to use 'as' syntax
lint: Improve camel case suggestion when empty.
doc: remove trailing shell prompts

because eyesore
doc: remove misleading/confusing info

We have to specify the module and the function name in the example where
the module shares a crate with the executable as well, so remove the
redundant (and potentially confusing) mention.
Adopting FFI changes for iOS
librustc: Restrict transmute intrinsicck to just rust-intrinsic fn's.
Add tests to make sure intrinsicck doesn't apply to non-intrinsic fn's.
auto merge of #16720 : tshepang/rust/trailing-prompt, r=alexcrichton

because eyesore
Clarify what tx and rx mean

Add a short explanation of what tx and rx mean in terms of channels.
auto merge of #16742 : vhbit/rust/ios-ffi-fix, r=alexcrichton
rustdoc: Don't assume that a doc attribute was sugared: Fixes #15976

As of 8876ce44, `is_sugared_doc` is encoded in metadata, so there is no
need to assume that doc attributes came from sugared comments.
Use cargo run in more places
libcollections: In tests, remove some uses of deprecated methods and
unused imports.
add missing ! char to feature gate hint
auto merge of #16704 : flugsio/rust/fix-rustc-ice-lint-underscores-only, r=brson

Fix for type identifiers with only underscores (two or more), I assume they doesn't count as camel case.

```rust
type __ = int;

fn main() {
}
```

```
error: internal compiler error: unexpected failure
note: the compiler hit an unexpected failure path. this is a bug.
note: we would appreciate a bug report: http://doc.rust-lang.org/complement-bugreport.html
note: run with `RUST_BACKTRACE=1` for a backtrace
task 'rustc' failed at 'index out of bounds: the len is 0 but the index is 0', /home/rustbuild/src/rust-buildbot/slave/nightly-linux/build/src/librustc/lib.rs:1

stack backtrace:
   1: 0xb603f5d0 - rt::backtrace::imp::write::ha55f265f6626471dmxr
   2: 0xb6042620 - failure::on_fail::h4d2c6d42b67e94803Sr
   3: 0xb640a180 - unwind::begin_unwind_inner::h484879fa7cc3611fZhe
   4: 0xb6409e50 - unwind::begin_unwind_fmt::hd14e5c64bc9006capfe
   5: 0xb6409df0 - rust_begin_unwind
   6: 0xb6454580 - failure::begin_unwind::h9ab1fc5753bd08f3YDk
   7: 0xb6458cb0 - failure::fail_bounds_check::h88167bad36865909aCk
   8: 0xb6f685d0 - lint::builtin::NonCamelCaseTypes.LintPass::check_item::check_case::he854eeffd105cb0f40E
   9: 0xb6f68050 - lint::builtin::NonCamelCaseTypes.LintPass::check_item::hc35b45d248e41cd43XE
  10: 0xb6f7b760 - lint::context::Context<'a>.Visitor<(*>::visit_item::closure.139262
  11: 0xb6f79510 - lint::context::Context<'a>::with_lint_attrs::hb9efe321fa321ce6spG
  12: 0xb6f81d30 - lint::context::Context<'a>.Visitor<(*>::visit_mod::he4593c831936b308ZMG
  13: 0xb6f8f2f0 - lint::context::check_crate::closure.139319
  14: 0xb6f79510 - lint::context::Context<'a>::with_lint_attrs::hb9efe321fa321ce6spG
  15: 0xb6efda70 - lint::context::check_crate::ha9e64328726b9579q1G
  16: 0xb6efda20 - driver::driver::phase_3_run_analysis_passes::closure.136263
  17: 0xb659d640 - util::common::time::h2837683151147173214
  18: 0xb6e7d130 - driver::driver::phase_3_run_analysis_passes::h7079eff53afc4de3Jfz
  19: 0xb6e783f0 - driver::driver::compile_input::h0ec84a550e24779cP1y
  20: 0xb6f26250 - driver::run_compiler::h7e7c01ecbfd0ad87JzC
  21: 0xb6f26150 - driver::main_args::closure.137215
  22: 0xb6f380d0 - task::TaskBuilder<S>::try_future::closure.138376
  23: 0xb6f37ec0 - task::TaskBuilder<S>::spawn_internal::closure.138353
  24: 0xb774bdd0 - task::spawn_opts::closure.8325
  25: 0xb6409c10 - unwind::try::try_fn::h91f00772748cf73eD8d
  26: 0xb6468ae0 - rust_try_inner
  27: 0xb6468aa0 - rust_try
  28: 0xb6407880 - unwind::try::h78a4fc0e85c326aef6d
  29: 0xb6407640 - task::Task::run::hb6f2d9484116e3d8xcd
  30: 0xb774bba0 - task::spawn_opts::closure.8271
  31: 0xb6409350 - thread::thread_start::h8c02fef9f651da5cjBd
  32: 0xb5ed3fc0 - start_thread
  33: 0xb62e8a32 - __clone
  34:        0x0 - <unknown>
```
glob: Deprecate the library in favor of cargo

This library has been moved out to a cargo package in rust-lang.
auto merge of #16685 : alexcrichton/rust/remove-glob, r=brson

This library has been moved out to a cargo package in rust-lang.