Allow skipping URL rewrite and redirect on error

The import fancybox does not reopen in the case of an import error, even if the import method catches the error and attaches a message to the form.

This is due to the fact that the URL service performs a redirection after this error, hence the original error message is lost.

To handle this use case, the fancy redirect should be avoided in this case (which is already the case when a standard validation error occurs, since the JSF postback prevents the request from being redirected.