Pass dataIndex and series arguments to the symbol function, to allow shapes to vary by the original data.

Based on my example here - http://stevesrunningcharts.apphb.com/
I wanted to be able to draw the more recent points in the chart larger.

Two commits are included - 
1. A bug fix. The axisOptions.axisLabel statements were blowing up, because the axisOptions hadn't been $.extend'ed yet. So I moved the $.extend's up in the code.
2. I added a couple arguments to the symbol(...) call - dataIndex, and series. dataIndex maps directly to the index of the original data source that is currently being drawn; series is so that I can tell which original data source to look at. 

There is another similar pull request out there...but it didn't pass the series, so I couldn't figure out how to find the item in the original data source.

Let me know what you think!