Fix incorrect replacement of `modulo` with `rem`
Move impls of `Num` out of core::num and clean up imports
Use #[cfg(not(stage0))] to exclude items from stage0

As requested on the mailing list: https://mail.mozilla.org/pipermail/rust-dev/2013-April/003713.html
Rename Natural to Integer

'Natural' normally means 'positive integer' in mathematics. It is therefore strange to implement it on signed integer types. 'Integer' is probably a better choice.
Use borrowed pointers for Integer methods

This brings them in line with the quot and rem traits, and is be better for large Integer types like BigInt and BigUint because they don't need to be copied unnecessarily.
Add Fractional, Real and RealExt traits
core: Comments only -- move FIXME to correct location
rustpkg: update README saying which tests pass
rustpkg: Make path searching work as described in the rustpkg doc

rustpkg now searches for package directories in ./src rather than
in . . I also added a rudimentary RUST_PATH that's currently
hard-wired to the current directory. rustpkg now uses src/, lib/,
and build/ directories as described in the manual.

Most of the existing test scenarios build now; the README file
(in a separate commit) explains which ones.
rustpkg: Correct directory structure in test scenarios
rustpkg: Preliminary work on install command

Mostly just tests (that are ignored); install command is still
stubbed out.
Restore Round trait and move appropriate methods out of Real
Update impl of Round for Ratio
Add basic documentation for with_capacity
Move documentation for vec::windowed where it will be generated
Rename vec::mod2 to vec::mod_zip
rt: pull upstream ISAAC code for consistency between 32/64 bit platforms

The "unsigned 4 byte" `ub4`s are actually 8 bytes on 64-bit platforms
which mean that some bits > 2**32 were retained in calculations, these
would then "reappear" after a shift and so the stream of random numbers
would differ on 32 bit vs 64 bit platforms.
Made fail! and assert! accept both &'static str and ~str, as well as a fmt! like format list.

Unwinding through macros now happens as a call to the trait function `FailWithCause::fail_with()`, which consumes self, allowing to use a more generic failure object in the future.
auto merge of #6048 : bjz/rust/numeric-traits, r=pcwalton

As part of the numeric trait reform (see issue #4819), I have added the following traits to `core::num` and implemented them for floating point types:

~~~rust
pub trait Round {
    fn floor(&self) -> Self;
    fn ceil(&self) -> Self;
    fn round(&self) -> Self;
    fn trunc(&self) -> Self;
    fn fract(&self) -> Self;
}

pub trait Fractional: Num
                    + Ord
                    + Round
                    + Quot<Self,Self> {
    fn recip(&self) -> Self;
}

pub trait Real: Signed
              + Fractional {
    // Common Constants
    fn pi() -> Self;
    fn two_pi() -> Self;
    fn frac_pi_2() -> Self;
    fn frac_pi_3() -> Self;
    fn frac_pi_4() -> Self;
    fn frac_pi_6() -> Self;
    fn frac_pi_8() -> Self;
    fn frac_1_pi() -> Self;
    fn frac_2_pi() -> Self;
    fn frac_2_sqrtpi() -> Self;
    fn sqrt2() -> Self;
    fn frac_1_sqrt2() -> Self;
    fn e() -> Self;
    fn log2_e() -> Self;
    fn log10_e() -> Self;
    fn log_2() -> Self;
    fn log_10() -> Self;

    // Exponential functions
    fn pow(&self, n: Self) -> Self;
    fn exp(&self) -> Self;
    fn exp2(&self) -> Self;
    fn expm1(&self) -> Self;
    fn ldexp(&self, n: int) -> Self;
    fn log(&self) -> Self;
    fn log2(&self) -> Self;
    fn log10(&self) -> Self;
    fn log_radix(&self) -> Self;
    fn ilog_radix(&self) -> int;
    fn sqrt(&self) -> Self;
    fn rsqrt(&self) -> Self;
    fn cbrt(&self) -> Self;

    // Angular conversions
    fn to_degrees(&self) -> Self;
    fn to_radians(&self) -> Self;

    // Triganomic functions
    fn hypot(&self, other: Self) -> Self;
    fn sin(&self) -> Self;
    fn cos(&self) -> Self;
    fn tan(&self) -> Self;

    // Inverse triganomic functions
    fn asin(&self) -> Self;
    fn acos(&self) -> Self;
    fn atan(&self) -> Self;
    fn atan2(&self, other: Self) -> Self;

    // Hyperbolic triganomic functions
    fn sinh(&self) -> Self;
    fn cosh(&self) -> Self;
    fn tanh(&self) -> Self;
}

/// Methods that are harder to implement and not commonly used.
pub trait RealExt: Real {
    // Gamma functions
    fn lgamma(&self) -> (int, Self);
    fn tgamma(&self) -> Self;

    // Bessel functions
    fn j0(&self) -> Self;
    fn j1(&self) -> Self;
    fn jn(&self, n: int) -> Self;
    fn y0(&self) -> Self;
    fn y1(&self) -> Self;
    fn yn(&self, n: int) -> Self;
} 
~~~

The constants in `Real` could be [associated items](http://smallcultfollowing.com/babysteps/blog/2013/04/03/associated-items-continued/) in the future (see issue #5527). At the moment I have left the constants in `{float|f32|f64}::consts` in case folks need to access these at compile time. There are also instances of `int` in `Real` and `RealExt`. In the future these could be replaced with an associated `INTEGER` type on `Real`.

`Natural` has also been renamed to `Integer`. This is because `Natural` normally means 'positive integer' in mathematics. It is therefore strange to implement it on signed integer types. `Integer` is probably a better choice.

I have also switched some of the `Integer` methods to take borrowed pointers as arguments. This brings them in line with the `Quot` and `Rem` traits, and is be better for large Integer types like `BigInt` and `BigUint` because they don't need to be copied unnecessarily.

There has also been considerable discussion on the mailing list and IRC about the renaming of the `Div` and `Modulo` traits to `Quot` and `Rem`. Depending on the outcome of these discussions they might be renamed again.
auto merge of #6054 : catamorphism/rust/rustpkg, r=graydon

r? @graydon

Sorry, this pull request is a few different things at once, but I tried to make them separate commits.

First, as before, this should do file searching the way that's described in the doc now.

Second, there's also some preliminary work on the install command (really just tests for it).