Reworked Canvas 2D API using our revised DrawFocusRing

I rewrote the the canvas 2D API code on drawFocusRing. This one:

- Uses our API modification for drawFocusRing() which needs to be
implemented (call is commented out for the time being so I have substituted
the drawing calls)
- Works in IE 9 for the shadow DOM. The one in the spec did not run in IE
do to a few unsupported methods and coding errors.
- Sets Focus on the appropriate checkboxes when the corresponding canvas
checkbox is clicked with the mouse. This does not work yet in Safari, FF or
Chrome as they don't yet support keyboard focus in the DOM subtree. Safari
and Chrome are probably dependent on a webkit update.
- Has comments for others to see what we are trying to do

Keyboard support will not work in FF 4 as keyboard navigation of the DOM
subtree does not work yet. I have not yet run this with a screen reader (I
don't have a screen reader running on my Windows 7 machine - yet) and a
magnifier will not work until we implement drawFocusRing(0

Before I put this in our modifications to the canvas2DAPI change proposal
we need group sign off on the modifications.

David, this is a good test example for when you get to implementing the DOM
subtree.

(See attached file: CanvasEditor.html)

Rich Schwerdtfeger
CTO Accessibility Software Group