Implements [RFC 474](https://github.com/rust-lang/rfcs/pull/474); see
that RFC for details/motivation for this change.

This initial commit does not include additional normalization or
platform-specific path extensions. These will be done in follow up
commits or PRs.

Remove the old path.
Rename path2 to path.
Update all clients for the new path.

Also make some miscellaneous changes to the Path APIs to help the
adoption process.

Closes #9467

Previously, any package would match any other package ID when searching
using the rust_path_hack, so long as the directory had one or more crate
files in it. Now, rustpkg checks that the parent directory matches the
package ID.

Closes #9273

The trait will keep the `Iterator` naming, but a more concise module
name makes using the free functions less verbose. The module will define
iterables in addition to iterators, as it deals with iteration in
general.

Note that I left dirname as returning ~str, because both of its
implementations work by calling dir_path, which produces a new path,
and thus we cannot borrow the result from &'a self passed to dirname
(because the new path returned by dir_path will not live long enough
to satisfy the lifetime 'a).

.with_c_str() is a replacement for the old .as_c_str(), to avoid
unnecessary boilerplate.

Replace all usages of .to_c_str().with_ref() with .with_c_str().

Previous dicussions about CString suggested that interior nulls should
throw an error. This was never implemented. Add this now, using a
condition (named null_byte) to allow for recovery.

Add method .to_c_str_unchecked() that skips this check.

cc #7887

This commit allows you to write:

 extern mod x = "a/b/c";

which means rustc will search in the RUST_PATH for a package with
ID a/b/c, and bind it to the name `x` if it's found.

Incidentally, move get_relative_to from back::rpath into std::path

this has been replaced by `for`

`rustpkg build`, if executed in a package source directory inside
a workspace, will now build that package. By "inside a workspace"
I mean that the parent directory has to be called `src`, and rustpkg
will create a `build` directory in .. if there isn't already one.

Same goes for `rustpkg install` and `rustpkg clean`.

For the time being, `rustpkg build` (etc.) will still error out if
you run it inside a directory whose parent isn't called `src`.
I'm not sure whether or not it's desirable to have it do something
in a non-workspace directory.

This should allow fewer symbols to be exported.

They evaluated the receiver twice. They should be added back with
`AddAssign`, `SubAssign`, etc., traits.

Unfortunately, the main test for this is ignored due to #7071.

Closes #5682

I removed the `static-method-test.rs` test because it was heavily based
on `BaseIter` and there are plenty of other more complex uses of static
methods anyway.

This fixes the strange random crashes in compile-fail tests.

This reverts commit 96cd61ad.

Conflicts:
	src/librustc/driver/driver.rs
	src/libstd/str.rs
	src/libsyntax/ext/quote.rs

std: make all strings Equiv-alent to each other, generalise Path.push_many to take any type of string.

The first acts on &str and is not nul-terminated, the last two act on strings
that are always null terminated (&'static str, ~str and @str).