libstd: denominator isn't quotient
libcore: Rand impls for tuples and ~/@ boxes
auto merge of #5994 : huonw/rust/rational-fail-message, r=thestinger

A pedantic correction; the quotient is the result of `a/b`, not `b`.
auto merge of #5995 : huonw/rust/core-rand-impls, r=pcwalton
cell: public field is unsafe

use core::cell;

fn main() {
    let x = cell::Cell(Some(~"foo"));
    let y = x.value.get_ref().get_ref();
    do x.with_mut_ref |z| { *z = None; }
    println(*y) // boom!
}
auto merge of #6003 : thestinger/rust/cell, r=nikomatsakis

```rust
use core::cell;

fn main() {
    let x = cell::Cell(Some(~"foo"));
    let y = x.value.get_ref().get_ref();
    do x.with_mut_ref |z| { *z = None; }
    println(*y) // boom!
}
```