page node id attribute value is reused in the grid examples

[becky]

To meet accessibility guidelines, there can not be any duplicate ids used in the markup on a page. The test_grid_layout.html page uses the same id, page-0, for the page div surrounding the actual grid content (see preparePageNode() in dojox/grid/_grid/scroller.js). I believe this is using the same id because we are using the same set of data for the 3 grid examples on this page. But, since there are separate copies of the data embedded into the page, it would be better to scope the id to the id of the grid itself. For example, grid3-page-0.

(hope this is making sense)

[sorvell]

(In [12846]) !strict fixes #5364 Page nodes in scroller are now prefixed by the grid id. This id is used only for informational purposes.