datagrid sorting keeps incorrect selection

[tanneman]

steps to reproduce

• Goto http://dojotoolkit.org/reference-guide/dojox/grid/DataGrid.html
• Open the example grid
• Select a row
• Click sort on a column

expected

• The selection stays on the row that shows the item first selected (or selection is cleared)

actual

• The selection stays on the row index

[tanneman]

The selection also persists when another store is set. (seems to me that the _clearData may clear the selection as well?)

[Evan]

Duplicate with #7304 which provided a fix:

"The selection persistence feature is still limited with

1. Key precondition - Store Identifier(id) is required since id is used for differentiating row items.
2. Known issue - might not be accurate if some unloaded rows are selected by range(e.g.SHIFT + click)

Usage - To turn on this, please set 'keepSelection' attribute to true, e.g.
<div dojoType="dojox.grid.DataGrid??" keepSelection = true .../> or
<div dojoType="dojox.grid.TreeGrid??" keepSelection = true .../> or
<div dojoType="dojox.grid.LazyTreeGrid??" keepSelection = true .../>"