Clean old rules

If a user upgrades from `1.3 —> 1.4. —> 1.5` the `htmlindexes` rule is left in the `rules` directory (guess how I found this). Resulting is this:
![jedhtmlindexes-bug](https://f.cloud.github.com/assets/186670/1510918/3354e46a-4a9a-11e3-9f67-efb23e583288.png)

This branch uses the `update()` method to clean out the old files if they exist. It also fixes a `Strict standards` error in the `loadLanguage()` of the `script.php`.