查询时，清空checkbox

checkbox的清空分两步：清空打勾样式和清空pages属性QU_PROJECT_STATE的值

代码：

//设置checkbox样式上的非选中，清空pages属性QU_PROJECT_STATE的值
 $("QU_PROJECT_STATE1").checked = false;
 $("QU_PROJECT_STATE2").checked = false;
 $("QU_PROJECT_STATE3").checked = false;
 $("QU_PROJECT_STATE4").checked = false;
 /*
  * mygrid.setSearchPar(searchJSO)时pages属性根据searchJSO赋值，
  * 当执行一次查询而不选中checkbox选项，searchJSO.QU_PROJECT_STATE为undefined
  * 此时pages的QU_PROJECT_STATE属性没有被赋值，保存的是上次查询的QU_PROJECT_STATE属性值
  * 上一次查询的QU_PROJECT_STATE属性值可能是非空且有效的
  * */
 pages.QU_PROJECT_STATE = "";