fix #6, and performance optimize for ie6/7
fix #6, and performance optimize for ie6/7

yibuyisheng/etpl,hadesdu/etpl,xutingting02/etpl,noikiy/etpl,hadesdu/etpl,ecomfe/etpl,ecomfe/etpl,longze/etpl,hadesdu/etpl,yibuyisheng/etpl,noikiy/etpl,xutingting02/etpl,xutingting02/etpl,yibuyisheng/etpl,longze/etpl,ecomfe/etpl,longze/etpl,noikiy/etpl