Removed: base_plugin_controller::callback_the_post() attachment support
Removed: base_plugin_controller::callback_save_post() attachment support
Removed: base_plugin_controller::callback_delete_post() attachment support
Removed: associated tests
Added: __construct() triggers error if at least one of content, callback, or view parameters is not specified
Fixed: improper property use
Modified: set_callback()- check to ensure callback function is a callable function
Added: Base_Model_Help_Tab object tests