syntax: Tighten search paths for inner modules

This is an implementation of RFC 16. A module can now only be loaded if the
module declaring `mod name;` "owns" the current directory. A module is
considered as owning its directory if it meets one of the following criteria:

* It is the top-level crate file
* It is a `mod.rs` file
* It was loaded via `#[path]`
* It was loaded via `include!`
* The module was declared via an inline `mod foo { ... }` statement

For example, this directory structure is now invalid

    // lib.rs
    mod foo;

    // foo.rs
    mod bar;

    // bar.rs;
    fn bar() {}

With this change `foo.rs` must be renamed to `foo/mod.rs`, and `bar.rs` must be
renamed to `foo/bar.rs`. This makes it clear that `bar` is a submodule of `foo`,
and can only be accessed through `foo`.

RFC: 0016-module-file-system-hierarchy
Closes #14180

[breaking-change]
adding move_iter() function to collections::treemap::TreeSet
Removed unnecessary transmute
Replaced Ord by TotalOrd in priority queue
Rename to_vec and to_sorted_vec
Refactored and renamed functions to avoid failure
Fix dead code warnings
Fix insert_ordered in DList
auto merge of #14122 : dagitses/rust/master, r=alexcrichton

This is my first patch and hopefully nothing controversial: just a straightforward forwarding of TreeMap::move_iter() as TreeSet::move_iter().
auto merge of #14276 : aochagavia/rust/pr, r=alexcrichton
Remove leading underscores in function signatures in a trait definition.
auto merge of #14288 : zwarich/rust/euv-underscore, r=alexcrichton
auto merge of #14251 : alexcrichton/rust/hierarchy, r=huonw

This is an implementation of RFC 16. A module can now only be loaded if the
module declaring `mod name;` "owns" the current directory. A module is
considered as owning its directory if it meets one of the following criteria:

* It is the top-level crate file
* It is a `mod.rs` file
* It was loaded via `#[path]`
* It was loaded via `include!`
* The module was declared via an inline `mod foo { ... }` statement

For example, this directory structure is now invalid

    // lib.rs
    mod foo;

    // foo.rs
    mod bar;

    // bar.rs;
    fn bar() {}

With this change `foo.rs` must be renamed to `foo/mod.rs`, and `bar.rs` must be
renamed to `foo/bar.rs`. This makes it clear that `bar` is a submodule of `foo`,
and can only be accessed through `foo`.

RFC: 0016-module-file-system-hierarchy
Closes #14180

[breaking-change]
Minor doc fixes in various places
auto merge of #14279 : aochagavia/rust/pr2, r=huonw

The breaking changes are:

* Changed `DList::insert_ordered` to use `TotalOrd`, not `Ord`
* Changed `PriorityQueue` to use `TotalOrd`, not `Ord`
* Deprecated `PriorityQueue::maybe_top()` (renamed to replace `PriorityQueue::top()`)
* Deprecated `PriorityQueue::maybe_pop()` (renamed to replace `PriorityQueue::pop()`)
* Deprecated `PriorityQueue::to_vec()` (renamed to `PriorityQueue::into_vec()`)
* Deprecated `PriorityQueue::to_sorted_vec()` (renamed to `PriorityQueue::into_sorted_vec()`)
* Changed `PriorityQueue::replace(...)` to return an `Option<T>` instead of failing when the queue is empty.


[breaking-change]
Fix typo in libcore
auto merge of #14291 : Sawyer47/rust/doc-fixes, r=alexcrichton
auto merge of #14292 : limeburst/rust/master, r=alexcrichton
Rename Result.unwrap_or_handle() to .unwrap_or_else()

Result.unwrap_or_handle() is the equivalent of Option.unwrap_or_else().
In the interests of naming consistency, call it the same thing.

[breaking-change]
auto merge of #14294 : kballard/rust/result_unwrap_or_else, r=alexcrichton

Result.unwrap_or_handle() is the equivalent of Option.unwrap_or_else().
In the interests of naming consistency, call it the same thing.

[breaking-change]