Compiler message need improve for OrdSliceExt::sort()

[liigo]

Code:

// #[deriving(Eq, Ord, PartialEq, PartialOrd)]
struct X { x: int }

pub fn main() {
    let mut b: Vec<X> = Vec::new();
    b.sort();
}

Error:

tmp.rs:6:7: 6:13 error: type `collections::vec::Vec<X>` does not implement any method in scope named `sort`
tmp.rs:6     b.sort();

The compiler should tell us, struct X doesn't implements Ord, at least.

[apasel422]

This is fixed (after changing the type of X.x to i32):

> rustc --version
rustc 1.3.0-nightly (e4e93196e 2015-07-14)
> rustc foo.rs
foo.rs:6:7: 6:13 error: the trait `core::cmp::Ord` is not implemented for the type `X` [E0277]
foo.rs:6     b.sort();
               ^~~~~~
foo.rs:6:7: 6:13 help: run `rustc --explain E0277` to see a detailed explanation

[Gankra]

Needs test?