Adding autocomplete=off which doesn't still supress firefox from autocompleting the super password field during install, annoying

https://developer.mozilla.org/en/How_to_Turn_Off_Form_Autocompletion#Exceptions_and_Recommended_Workarounds

git-svn-id: http://dev.piwik.org/svn/trunk@2070 59fd770c-687e-43c8-a1e3-f5a4ff64c105