Debug formatting for pointers is truncated

[SSheldon]

fn main() {
    let x = 0;
    let p = &x as *const i32;
    println!("{:?}, {:x}", p, p as usize);
}

This sample code prints 0x5a83172c, 7fff5a83172c, where the pointer's debug doesn't include the first 4 characters of its address.

My rustc version:

$ rustc --version --verbose
rustc 1.0.0-nightly (4db0b3246 2015-02-25) (built 2015-02-25)
binary: rustc
commit-hash: 4db0b32467535d718d6474de7ae8d1007d900818
commit-date: 2015-02-25
build-date: 2015-02-25
host: x86_64-apple-darwin
release: 1.0.0-nightly

[SSheldon]

Possibly related to #22700, the most recent change to the fmt module? cc @nrc

The formatting is what we'd see if the pointer were cast to a u32 instead of a usize.

[SSheldon]

Fixed in #22901