Argument requiring equals does not print = in help

[TimBednarzyk]

Rust Version

1.14.0

Affected Version of clap

2.21.1

Expected Behavior Summary

When calling arg.require_equals(true), the generated help message should show --arg=<VALUE>. Without the equals sign in the help message, the user will think to put a space and will be confused when that fails.

Actual Behavior Summary

The help message shows --arg <VALUE>

Sample Code

extern crate clap;

use clap::*;

fn main() {
  let matches = App::new("example")
    .arg(Arg::with_name("mode")
         .long("mode")
         .value_name("MODE")
         .require_equals(true)
         .default_value("foo")
         .possible_values(&["foo", "bar"])
         ).get_matches();

  if matches.value_of("mode").unwrap() == "foo" {
    println!("mode == foo");
  }
  else {
    println!("mode == bar");
  }
}

Debug output

[kbknapp]

Great point, I hadn't thought about that. This is a very simple fix. I'm away from my computer for a few days, but will knock this out first thing when I return. If anyone submits a PR, it's simply adding some lines to the Display implementation of OptBuilder.