std::iter: Introduce .by_ref() adaptor

Creates a wrapper around a mutable reference to the iterator.

This is useful to allow applying iterator adaptors while still
retaining ownership of the original iterator value.

Example::

   let mut xs = range(0, 10);
   // sum the first five values
   let partial_sum = xs.by_ref().take(5).fold(0, |a, b| a + b);
   assert!(partial_sum == 10);
   // xs.next() is now `5`
   assert!(xs.next() == Some(5));
std::rt::uv::net: Handle `read_start` error

cc #9605
std::rt: Add NotConnected to IoErrorKind
rt::io::net::tcp: Fix eof_twice tests on Win32

cc #8811
extra: implement Encodable/Decodable for Uuid
Refine privacy error messages to be more accurate

This stops labeling everything as "is private" when in fact the destination may
be public. Instead, the clause "is inaccessible" is used and the private part of
the flag is called out with a "is private" message.

Closes #9793
std::rt: Fix the set up of the main thread so that it doesn't try to steal work

This is causing really awful scheduler behavior where the main thread scheduler is
continually waking up, stealing work, discovering it can't actually run the work,
and sending it off to another scheduler.
rustdoc: Use privacy visibility for pruning

This commit ends rustdoc's approximation of privacy and instead uses the result
of the various compiler passes instead.

Closes #9827
rustdoc: Don't abort if there's nothing to document

Instead there's no index.html file emitted because there wasn't anything to
document.

Closes #9828
fix bounds checking failure message

casting the `uint` to an `int` can result in printing high values as
negative intege
fix overflow on bounds checks

Closes #9020
use element count in slices, not size in bytes

This allows the indexing bounds check or other comparisons against an
element length to avoid a multiplication by the size.
remove executable flag from source file
Initial sketching out of the new path module

Define the basic types, and the GenericPath trait.

This module is currently called path2. It will be renamed later.
path2: Implement PosixPath

Fixes #5389 (new conventions for Path constructor)
path2: Start reimplementing in terms of ~[u8] instead of ~str

As documented in #7225, we cannot rely on paths being representable in
utf-8. Specifically, Linux allows anything (besides NUL) in a path.
Redesign GenericPath in light of this.

PosixPath hasn't been reimplemented yet for ~[u8].
path2: Reimplement PosixPath in terms of ~[u8]
path2: Update all the tests for the new [u8]-based approach
path2: Add tests for the [u8]-based methods
path2: Extract posix/windows into their own files

Move PosixPath into posix::Path.