bug 982006

* Use new error nsresult values in download notifications.
* Update mock_download_ui.js based on addition of 'ERRORS' to DownloadUI.
* added tests for new Downloads API errors in download notifications test
* added new tests for modal dialog changes in app modal dialog test
* AppModalDialog will ignore titles that contain the application URL or origin and instead
  use the app name if it is available. If not, it will simply use an empty string.

r=alive, crdlc
Merge pull request #17303 from nullaus/bug982006

bug 982006