* Fixed bug preventing two roles of same name, but of different plots, each interpolating its measure.
* Added the ability to not specify the "plot2" option, being sufficient to specify a spec for the plot named "plot2" in the "plots" option.
* Changed the initialization of plots, adding the "pvc.visual.Plot#initEnd" method, so that visual roles can be defined safely only after options from "plots" specs have been processed. There were problems in certain options not taking effect when given in the "plots" specs.
* Fixed a bug in the processing of plot2SeriesIndexes revealed by latest changes to the way interpolation copies atoms to newly interpolated datums. A calculation is always needed, even if plot2SeriesIndexes is used, so that interpolated datums are assigned the correct dataPart. The "dataPart" is not part of the grouping used by the interpolations.