弥补ExtJs CheckboxSelectionModel不能级联的自定义控件
由于 ExtJS 在做CheckboxSelectionModel的时候，没有考虑到会存在二级 三级等多级级联，导致目前存在做级联的时候，选择上级，往往会把下级 下下级选中，而实际上并没有被选中，只是视觉上view被选中了而已。项目中遇到此种情况，本来想改变界面原型的，单需求就这个样，改纠结了，一郁闷之下，将CheckboxSelectionModel的源代码做了修改，在使用的时候，需要将js和css一并引用：
js：

/* * Ext JS Library 2.0.0 * created by:raoyifeng * created at:2012-03-01 * licensing@extjs.com *  */Ext.grid.MyCheckboxSelectionModel = Ext.extend(Ext.grid.RowSelectionModel, {    header: '<div name="code">.x-grid3-hd-row td,.x-grid3-row-my td,.x-grid3-summary-row td{font:normal 11px arial,tahoma,helvetica,sans-serif;-moz-outline:none;-moz-user-focus:normal;}.x-grid3-row-my td,.x-grid3-summary-row td{line-height:13px;vertical-align:top;padding-left:1px;padding-right:1px;-moz-user-select:none;}.x-grid3-row-my .x-grid3-marker{padding:3px;}.x-grid3-row-my{cursor:default;border:1px solid #ededed;border-top-color:#fff;width:100%;}.x-grid3-row-checker-my,.x-grid3-hd-checker-my{width:100%;height:18px;background-position:2px 2px;background-repeat:no-repeat;background-color:transparent;background-image:url(images/row-check-sprite.gif);}.x-grid3-row-my .x-grid3-row-checker-my{background-position:2px 2px;}.x-grid3-row-selected-my .x-grid3-row-checker-my,.x-grid3-hd-checker-on-my .x-grid3-hd-checker-my{background-position:-23px 2px;}.x-grid3-hd-checker-my{background-position:2px 3px;}.x-grid3-hd-checker-on-my .x-grid3-hd-checker-my,.x-grid3-row-checker-on-my{background-position:-23px 3px;}.x-grid3-row-checker-my, .x-grid3-hd-checker-my {    width:100%;    height:18px;    background-position:2px 2px;    background-repeat:no-repeat;    background-color:transparent; background-image:url(images/row-check-sprite.gif);}.x-grid3-row-my .x-grid3-row-checker-my {    background-position:2px 2px;}.x-grid3-row-selected-my .x-grid3-row-checker-my, .x-grid3-hd-checker-on-my .x-grid3-hd-checker-my {    background-position:-23px 2px;}.x-grid3-hd-checker-my {    background-position:2px 3px;}.x-grid3-hd-checker-on-my .x-grid3-hd-checker-my, .x-grid3-row-checker-on-my{    background-position:-23px 3px;}.x-grid3-hd-row-my td, .x-grid3-row-my-my td, .x-grid3-summary-row-my td{font:normal 11px arial, tahoma, helvetica, sans-serif;    -moz-outline: none;-moz-user-focus: normal;}.x-grid3-row-my td, .x-grid3-summary-row-my td {    line-height:13px;    vertical-align: top;padding-left:1px;    padding-right:1px;    -moz-user-select: none;}.x-grid3-row-my .x-grid3-marker-my {    padding:3px;}.x-grid3-row-my {cursor: default;    border:1px solid #ededed;    border-top-color:#fff;    /*border-bottom: 1px solid #ededed;*/    width:100%;}.x-grid3-row-checker-on-my{    background-position:-23px 3px;}