1) I replaced useYAxisRange and yAxisRange with useYAxisTickSpacing and
   yAxisTickSpacing in the multi curve plot.

2) I modified the code in the multi curve plot that calculates the
   minimum and maximum of the data to exclude values where the marker
   variable was negative (A negative value in the marker variable
   indicates that the variable is invalid and should not be displayed).

3) I modified the multi curve plot so that it would also accept as
   input a collection of poly data data sets representing the individual
   curves to display.



git-svn-id: http://visit.ilight.com/svn/visit/trunk/src@6458 18c085ea-50e0-402c-830e-de6fd14e8384