改变Ext tree node的节点图标

[{id:'8', text:'process', iconCls:'tree-folder-node',children:[
{id:'19',text:'task', iconCls:'tree-leaf-node',leaf:true}]},
{id:'3', text:'host'}]

.x-tree-node-collapsed .tree-folder-node{
	background-image:url(images/folderICON.png);
}
.x-tree-node-leaf .tree-leaf-node{
	background-image:url(images/leafICON.png);
}