scatterChart bug fixes

I've fixed two bugs in the scatterChart model: data won't filter correctly when you enable fisheye, and pointer-events aren't initialized.

Fiddle http://jsfiddle.net/qggT8/1/ displays those problems and fiddle http://jsfiddle.net/qggT8/3/ has them fixed. Please contact me if you need any further details and thanks for your work.