5.4 build 1494 - Hotfix to previous build

• Fixed plugins using MySQL that started after Plan from breaking due to Plan unregistering the MySQL driver (Thanks for the fix Vankka!)

There were three things that lead to this issue not being caught:

• The driver unregistering previously dealt with other plugins using Plan driver was forgotten when writing driver download code
• The driver downloading changed so that the mysql driver was not relocated to plan.com.mysql.driver.Driver which caused the main MySQL driver to be unregistered instead
• There was no test environment in which a plugin using MySQL started after Plan

Sorry for any trouble this may have caused.