Prevent default built-in scripts from breaking minification groups. #9 #...

It seems like WP default scripts don't get assigned a `group` value after all, the final argument of the call to register the admin-bar.js script is never used to assign the `group` data value, same goes for all other default scripts:

https://github.com/WordPress/WordPress/blob/master/wp-includes/script-loader.php#L327 :
https://github.com/WordPress/WordPress/blob/master/wp-includes/class.wp-dependencies.php#L127

unlike what wp_enqueue_script does:
`if ( $in_footer )	$wp_scripts->add_data( $_handle[0], 'group', 1 );`
https://github.com/WordPress/WordPress/blob/master/wp-includes/functions.wp-scripts.php#L157

So the solution here is to detect the `dep->args` value if no `extra['group']` is available, cause they're basically the same thing.