Asset Wizard should notify users with no permissions to create Assets of this problem

Problem Description:

User roles where Access Asset Wizard permission is enabled while the Create Assets permissions are disabled may be wondering what is going on as clicking on 'New Directory' and 'New File' links in the Asset Wizard accomplishes nothing. A progress bar is displayed briefly, after which the user is returned to the same screen. A better approach would be some indication that their role does not have permissions to create Assets.

To Reproduce:
1. Follow the steps in http://drupal.org/node/239885
2. Once the Asset Wizard window pops up, click on New File or New Directory.