Fixed Directory->except to correctly handle excluded files

Fixed Directory->except to treat excluded files as patterns since the array assets is relative to the compiled version and not the source version.

This helps to improve performance on https://github.com/andrew13/Laravel-4-Bootstrap-Starter-Site by excluding .jshintrc from compilation

```php
'public' => function($collection)
{
	$collection->directory('assets/css', function($collection)
	{
		$collection->add('less/master.less')->apply('Less');
	})->apply('UriRewriteFilter')->apply('CssMin');

	$collection->directory('assets/js', function($collection)
	{
		$collection->javascript('jquery/jquery.min.js');
		$collection->add('bootstrap/bootstrap.js');
		$collection->requireDirectory('../../../vendor/twbs/bootstrap/js')->except('.jshintrc');
	})->apply('JsMin');
}
```