 * Dropped scale hsv, hcl and rgb, because perceptually, they are terrible (plus I never used them - if you have been, please let me know)

 * ggplot now deals nicely with facets which don't contain any data
 * fixed problem with legend space - everything should fit nicely now
 * errorbars should be much more robust now

 * id/grouping completely rewritten so that automatically grouped when any of the aesthetics is a categorical variable.  This behaviour is defined in the Grammar of Graphics, and makes things like qplot(wt, data=mtcars, geom="density", colour=factor(cyl)) work nicely
