New Guide: Ownership

This replaces the previous "Lifetimes guide," since we are discussing
things from an owernship perspective now.
Remove outdated comment.

https://github.com/rust-lang/rust/pull/19472#issuecomment-65370278
Overload the `==` operator

- String == &str == CowString
- Vec ==  &[T] ==  &mut [T] == [T, ..N] == CowVec
- InternedString == &str
Replace `equiv` method calls with `==` operator sugar
Remove unused transmutes from tests
Fix fallout
Deprecate Equiv
rustdoc: Fixed a missing rendering of ForeignStaticItems.
rustdoc: Refactored various uses of ItemType.

In particular, ItemType variants are no longer reexported. Since
we already do namespace them via `item_type` mod, it's fine.
rustdoc: Removed Foreign{Function,Static} item types.

They are just (unsafe) functions and static items to most users
and even compilers! The metadata doesn't distinguish them, so Rustdoc
ended up producing broken links (generated `ffi.*.html`, links to
`fn.*.html`). It would be best to avoid this pitfall at all.
rustdoc: Avoid rendering foreign items to the sidebar.

Otherwise the generated documentation is 30% larger. The sidebar
renders an entry for each item to all items, so large modules have
O(n^2) items rendered in the sidebars. Not a correct solution, but
at least it works.
test: Ignore issue-19501 pretty for now

I don't have enough time to investigate this thoroughly, so for now let's get
the queue moving by ignoring this test.

cc #19501
Remove feature gates for `if let`, `while let`, and tuple indexing

Closes #19469
make fmt_macros and rustdoc have standard doc attributes
auto merge of #19502 : alexcrichton/rust/issue-19501, r=sfackler

I don't have enough time to investigate this thoroughly, so for now let's get
the queue moving by ignoring this test.

cc #19501
whitespace cleanup
rustup: make rustup executable
rustup: probe for the existance of tar
rustup: add a RUST_ prefix to the rust-specific variables
rustup: rename TMP_DIR to CFG_TMP_DIR