Passed options should override defaults.

When invoking a reporter with custom options, one must specify _ALL_ options instead of just specifying the option or options they wish to override. This is due to the fact that instead of merging the default options in nodeunit.json with the passed-in options, the passed options are just used wholesale (`if (!options) {`, etc).

It would be super-cool if the passed options would simply override the defaults in nodeunit.json.

Thanks!