called when a script has finished executing
function chain_script_executed(script_obj,chain_group) {
				if (chain_opts[_Debug]) log_msg("script execution finished: "+script_obj.real_src);
				script_obj.ready = script_obj.finished = true;
				script_obj.exec_trigger = null;
				// check if chain group is all finished
				for (var i=0; i<chain_group.scripts.length; i++) {
					if (!chain_group.scripts[i].finished) return;
				}
				// chain_group is all finished if we get this far
				chain_group.finished = true;
				advance_exec_cursor();
			}