Include import name in import shadowing error messages.

This partially alleviates the confusing behavior in issue #16597
Update compile-fail tests due to changed diagnostics
Add compile-fail test for missing import shadowing case
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).
Always insert methods into the search index, even if we're currently in a private module.

Previously, this caused methods of re-exported types to not be inserted into
the search index. This fix may introduce some false positives, but in my
testing they appear as orphaned methods and end up not being inserted into the
final search index at a later stage.

Fixes issue #11943
libcollections: In tests, remove some uses of deprecated methods and
unused imports.
add missing ! char to feature gate hint
Add a simple test for rustdoc search index contents
debuginfo: Allow to activate GDB pretty printers in autotests.
debuginfo: Add GDB pretty printers for structs and enums.
debuginfo: Emit different autotest debugger scripts depending on GDB version.
debuginfo: Improve GDB version handling in compiletest tool
Allow a regex filter for RUST_LOG

When specifying RUST_LOG, the programmer may append `/regex` to the end of the spec. All results will then be filtered using that regex.
stabilize core::option

Per API meeting

  https://github.com/rust-lang/meeting-minutes/blob/master/Meeting-API-review-2014-08-13.md

Most of the module is marked as stable or unstable; most of the unstable
items are awaiting resolution of conventions issues.

However, a few methods have been deprecated, either due to lack of use
or redundancy:

* `take_unwrap`, `get_ref` and `get_mut_ref` (redundant, and we prefer
  for this functionality to go through an explicit .unwrap)
* `filtered` and `while`
* `mutate` and `mutate_or_set`
* `collect`: this functionality is being moved to a new `FromIterator`
  impl.

Due to deprecations, this is a:

[breaking-change]
Fallout from stabilizing core::option
stabilize core::result

Per API meeting

  https://github.com/rust-lang/meeting-minutes/blob/master/Meeting-API-review-2014-08-13.md

Most of the module is marked as stable or unstable; most of the unstable
items are awaiting resolution of conventions issues.

* `collect`: this functionality is being moved to a new `FromIterator`
  impl.
* `fold_` is deprecated due to lack of use
* Several methods found in `core::option` are added here, including
  `iter`, `as_slice`, and variants.

Due to deprecations, this is a:

[breaking-change]
Fix regionck to consider bounds on a proc when capturing variables
Fix regionck to account for the uniqueness requirements on ref mut reborrows
Fix kindck to consider inherited bounds