Add traits for primitive numeric types

As part of the numeric trait reform (see issue #4819), I have added the following traits to `core::num` and implemented them for Rust's primitive numeric types:

~~~rust
pub trait Bitwise: Not<Self>
                 + BitAnd<Self,Self>
                 + BitOr<Self,Self>
                 + BitXor<Self,Self>
                 + Shl<Self,Self>
                 + Shr<Self,Self> {}

pub trait BitCount {
    fn population_count(&self) -> Self;
    fn leading_zeros(&self) -> Self;
    fn trailing_zeros(&self) -> Self;
}

pub trait Bounded {
    fn min_value() -> Self;
    fn max_value() -> Self;
}

pub trait Primitive: Num
                   + NumCast
                   + Neg<Self>
                   + Add<Self,Self>
                   + Sub<Self,Self>
                   + Mul<Self,Self>
                   + Quot<Self,Self>
                   + Rem<Self,Self> {
    fn bits() -> uint;
    fn bytes() -> uint;
}

pub trait PrimitiveInt: Integer
                      + Primitive
                      + Bounded
                      + Bitwise
                      + BitCount {}

pub trait Uint: PrimitiveInt
              + Unsigned {}

pub trait Int: PrimitiveInt
             + Signed {}

pub trait Float: Real
               + Signed
               + Primitive {
    fn NaN() -> Self;
    fn infinity() -> Self;
    fn neg_infinity() -> Self;
    fn neg_zero() -> Self;

    fn is_NaN(&self) -> bool;
    fn is_infinite(&self) -> bool;
    fn is_finite(&self) -> bool;
}
~~~
Note: I'm not sure my implementation for `BitCount::trailing_zeros` and `BitCount::leading_zeros` is correct for uints. I also need some assistance creating appropriate unit tests for them.

More work needs to be done in implementing specialized floating-point and integer functions for primitive functions, but I'm beginning to reach the limits of my knowledge. Please leave your suggestions/critiques/ideas on #4819 if you have them – I'd very much appreciate hearing them.