[CDF-372] - CCC - The new pointing mode, "near", is not working satisfactorily

* New protovis version with several improvements to the point behavior.
* Added max pointing radius to the legend markers, and to rule and label signs, in general.
* Fixed pointing instability problem in the tree map plot due to the existence off-sight nested rectangles.
* Updated documentation for the pointing options.
* Fixed issue where the HeatGrid would not show the tooltip when pointingMode=near

@pamval please review.