align in format! macro does not work with String as Debug

[ghost]

Playground url: https://play.rust-lang.org/?gist=1ff6c43dc1da08b05ad13bc772de070e&version=nightly&backtrace=0

fn main() {
    println!("{0: <10} | {1: <10?} | {2: <10} | {3: <10}",
             "total",
             "blanks",
             "comments",
             "code");
    println!("{0: <10} | {1: <10?} | {2: <10} | {3: <10}", 0, 0, 0, 0);
    println!("{0: <10} | {1: <10} | {2: <10?} | {3: <10}", 77, 0, 3, 74);
    println!("{0: <10?} | {1: <10} | {2: <10} | {3: <10?}",
             460,
             0,
             10,
             1371);
}

Align works properly for other types.

rustc 1.15.0-nightly (daf8c1dfc 2016-12-05)
total      | "blanks" | comments   | code      
0          | 0          | 0          | 0         
77         | 0          | 3          | 74        
460        | 0          | 10         | 1371      
Program ended.

without ?

fn main() {
    println!("{0: <10} | {1: <10} | {2: <10} | {3: <10}",
             "total",
             "blanks",
             "comments",
             "code");
    println!("{0: <10} | {1: <10?} | {2: <10} | {3: <10}", 0, 0, 0, 0);
    println!("{0: <10} | {1: <10} | {2: <10?} | {3: <10}", 77, 0, 3, 74);
    println!("{0: <10?} | {1: <10} | {2: <10} | {3: <10?}",
             460,
             0,
             10,
             1371);
}

rustc 1.15.0-nightly (daf8c1dfc 2016-12-05)
total      | blanks     | comments   | code      
0          | 0          | 0          | 0         
77         | 0          | 3          | 74        
460        | 0          | 10         | 1371      
Program ended.

[sinkuu]

This issue is a duplication of #30164.