Pretty printing brackets on match arms

[dbp]

Currently, the pretty printer prints the brackets for match arms (if they are blocks) on a new line. This means you get something like (omitting a bunch of repetitions to make it not all fit inline):

fn main() {
    match h {
      something =>
      {
          hello;
          ...
          hello;
      }
    }
}

This is because the block is printed with print_expr, which means the whole thing is wrapped inside of a box. What should happen is that the opening bracket should be in the head box with "something =>" (that's how it works elsewhere). With the code in this pull request, the same code is formatted as:

fn main() {
    match h {
      something => {
        hello;
        ...
        hello;
      }
    }
}

Which seems better.

Edit: Now that incoming is not burning, I can confirm that the code here does not cause any test failures.

[brson]

Thanks!