Added the date to a change log item.
* Tweaked: the demo plugin to load the admin-page object only in the administration pages with the is_admin() function.
* Fixed: a bug that setting and retrieving a transient for the field error array caused extra database queries.
* Fixed: a bug that setting multiple checkboxes caused undefined index warning.
* Fixed: a bug in the demo plugin that single upload field did not appear and caused undefined index warning after updating the options.