Use `+` instead of `:` for trait bounds in error messages.

[nrc]

Fixing this on my DST branch.

[ftxqxd]

In which error messages do bounds get printed with :? A quick test showed that trait objects work fine in error messages:

fn main() {
    let _: Box<Num+Send> = 1i;
}
// error: mismatched types: expected `Box<core::num::Num+Send>`, found `int` (expected box, found int)

Was this fixed, or is there some other case I’m missing?

[jdm]

DST landed, so presumably this was fixed.

[ftxqxd]

Can this issue be closed, then?

[steveklabnik]

Closing until proven not-guilty.

Or something.