core: Document core::path::GenericPath's trait methods
core: Use a better termination condition in os::mkdir_recursive

Instead of checking whether the parent is "." or "/", check the
number of components.

Also, more tests.
libstd: remove implicit copying of BigInt/BigUint
libstd: modify wrong shift width.

borrow = *elem << (uint::bits - n_bits);

The code above contains a bug that the value of the right operand of the shift operator exceeds the size of the left operand,
because sizeof(*elem) == 32, and 0 <= n_bits < 32 in 64bit architecture.

If `--opt-level` option is not given to rustc, the code above runs as if the right operand is `(uint::bits - n_bits) % 32`,
but if --opt-level is given, `borrow` is always zero.

I wonder why this bug is not catched in the libstd's testsuite (I try the `rustc --test --opt-level=2 bigint.rs` before fixing the bug,
but the unittest passes normally.)
Move appropriate functions out of Real and into separate Algebraic, Trigonometric, Exponential and Hyperbolic traits
Implement Fractional for Ratio
Rename 'divisible_by' method to 'is_multiple_of', add tests for 'is_odd' and 'is_even'
Merge Exponential and Hyperbolic traits

The Hyperbolic Functions are trivially implemented in terms of `exp`, so it's  simpler to group them the Exponential trait. In the future these would have default implementations.
Revert "Merge Exponential and Hyperbolic traits"

After discussions on IRC and #4819, we have decided to revert this change. This is due to the traits expressing different ideas and because hyperbolic functions are not trivially implementable from exponential functions for floating-point types.
auto merge of #6110 : bjz/rust/numeric-traits, r=pcwalton

As discussed on issue #4819, I have created four new traits: `Algebraic`, `Trigonometric`, `Exponential` and `Hyperbolic`, and moved the appropriate methods into them from `Real`.

~~~rust
pub trait Algebraic {
    fn pow(&self, n: Self) -> Self;
    fn sqrt(&self) -> Self;
    fn rsqrt(&self) -> Self;
    fn cbrt(&self) -> Self;
    fn hypot(&self, other: Self) -> Self;
}

pub trait Trigonometric {
    fn sin(&self) -> Self;
    fn cos(&self) -> Self;
    fn tan(&self) -> Self;
    fn asin(&self) -> Self;
    fn acos(&self) -> Self;
    fn atan(&self) -> Self;
    fn atan2(&self, other: Self) -> Self;
}

pub trait Exponential {
    fn exp(&self) -> Self;
    fn exp2(&self) -> Self;
    fn expm1(&self) -> Self;
    fn log(&self) -> Self;
    fn log2(&self) -> Self;
    fn log10(&self) -> Self;
}

pub trait Hyperbolic: Exponential {
    fn sinh(&self) -> Self;
    fn cosh(&self) -> Self;
    fn tanh(&self) -> Self;
}
~~~

There was some discussion over whether we should shorten the names, for example `Trig` and `Exp`. No abbreviations have been agreed on yet, but this could be considered in the future.

Additionally, `Integer::divisible_by` has been renamed to `Integer::is_multiple_of`.
Revert "libcore: remove unnecessary deref"

This reverts commit 9860fe10a19cc4997e58861df905f8dbe4de3c5b.
librustc: Remove `ptr::addr_of`.
librustc: Implement `reinterpret_cast` in terms of `transmute`.
librustc: Rename `reinterpret_cast` to `transmute_copy` and remove the intrinsic
librustc: Remove the legacy mode in the type visitor intrinsic.
libfuzzer: De-mode the fuzzer.
test: Remove #[legacy_modes] from the test suite.
librustc: Make `&fn` by-copy by default and remove the mode from `frame_address`.
librustc: Remove the concept of modes from the compiler.

This commit does not remove `ty::arg`, although that should be
possible to do now.
test: Fix tests.