Added simple navigation links between lineChart, StackedAreaChart and
CumulativeChart test examples.
Updating algorithm for calculating the tooltip offset positioning.
Created function to get the first non-svg parent element in tooltip.js.
Needed because in Firefox and IE, SVG.offsetParent does not exist.
Fixing a NASTY Microsoft IE bug I found during cross browser testing.
Mousing over SVG.rect returns wrong X,Y coordinates, but only in IE.