Fix _coffee REPL for CoffeeScript 1.7

Needs explicit `register()` call here too.

Before:

```
$ _coffee
> console.log require.extensions['.coffee'].toString()
function () {
          throw new Error("Use CoffeeScript.register() or require the coffee-script/register module to require " + ext + " files.");
        }
```

After:

```
$ _coffee
> console.log require.extensions['.coffee'].toString()
function (module, filename) {
    var answer;
    answer = CoffeeScript._compileFile(filename, false);
    return module._compile(answer, filename);
  }
```