plot.xbal fails if report = 'chisq'

[josherrickson]

This may be intended behavor, but if so, the terminology seems odds to me.

> plot(xBalance(pr ~ cost, data = nuclearplants))
> plot(xBalance(pr ~ cost, data = nuclearplants, report = 'all'))
> plot(xBalance(pr ~ cost, data = nuclearplants, report = 'chisq'))
Error in adrop.default(x$results, drop = 2) :
  dimensions to drop (2) do not have length 1

Seems that report really means compute. I had previously thought report to only be an argument passed to print.xbal, and that all three xbal objects were identical except their call.

Suggestions are either to deprecate report = for something like calculate or save, or making it behave like an actual report option.

(This came up for some slides I'm creating, I want to see xBalance output and plot, but the full output is too cluttered. However, I'm trying to avoid confusing users, so would prefer to avoid either running two xBalance calls or using print.xbal explicitly.)