MDL-19139 selectgroups formslib element improvements - 1/ does not validate if optgroup array empty 2/ add optional $showchoose parameter which adds "Choose..." as first item of list with empty value; merged from MOODLE_19_STABLE
MDL-19139 selectgroups formslib element improvements - 1/ does not validate if optgroup array empty 2/ add optional $showchoose parameter which adds "Choose..." as first item of list with empty value; merged from MOODLE_19_STABLE

dilawar/moodle