called when a script has finished preloading
function chain_script_ready(script_obj,exec_trigger) {
				if (chain_opts[_Debug]) log_msg("script preload finished: "+script_obj.real_src);
				script_obj.ready = true;
				script_obj.exec_trigger = function() {
					if (chain_opts[_Debug]) log_msg("script execute start: "+script_obj.real_src);
					exec_trigger();
				}
				advance_exec_cursor(); // will only check for 'ready' scripts to be executed
			}