add an `abort` intrinsic

This should be preferred to the libc `abort` function.
auto merge of #9860 : thestinger/rust/abort, r=Aatch

This should be preferred to calling the libc `abort` function.
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
Remove extra::flatpipes

Closes #9884
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.
path2: Add more tests to posix impl
path2: Update for changes from master
path2: Implement WindowsPath
path2: Rename Path::new() to Path::from_vec()
path2: Add opt variants for from_vec/from_str
path2: Implement .as_display_str() and .to_display_str()

These functions are for working with a string representation of the path
even if it's not UTF-8 encoded. They replace invalid UTF-8 sequences
with the replacement char.