XYPlot rendering logic in jfreechart-fse 1.0-SNAPSHOT

[david.gilbert]

I'd like to persist a little with the map based approach for JFreeChart 2, since I think it can provide some flexibility for (a) mapping datasets to renderers and axes and (b) reordering items for presentation purposes. However, in JFreeChart 1.0.x the API is definitely index based, so there is less scope there to make it work with generalised keys (for JFreeChart 2 I don't mind changing the API).

I'm starting some work on getting JFreeChart 1.0.20 released (mainly to improve the JavaFX support) soon, so let's try to get the bugs you have pointed out either fixed for 1.0.20 or 1.0.21.