Integer constant treated as 16 bit

[d3zd3z]

The following code prints 16959 instead of 999999 (999999 & 0xFFFF == 16959).

fn main() {
    let mut count = 0;
    for 999_999.times() {
        count += 1;
    }
    io::println(fmt!("%u", count));
}

Tested as of 09bb07b (I'm building tip now to reteset)

[nikomatsakis]

Dup of #3211 (but thank you!)