Uses visual style for long closure arguments

rustfmt seems to use visual style rather than block style when reformatting long closure argument lists:

    let write_status = |status: &mut Vec<ansi_term::ANSIString>,
                        diff: &Diff,
                        heading: &str,
                        color: &Style,
                        show_hints: bool,
                        hints: &[&str]|
     -> Result<bool> {

One possible block-style alternative rustfmt could use:

    let write_status = |
        status: &mut Vec<ansi_term::ANSIString>,
        diff: &Diff,
        heading: &str,
        color: &Style,
        show_hints: bool,
        hints: &[&str]
    | -> Result<bool> {

Start by reproducing the rustfmt formatting shown for a closure with a long argument list. Compare the current visual style with the proposed block style; done means rustfmt consistently applies the intended style and covers this formatting case with a regression check.