[R] Histogram with equal-counts (-probability)

[Hamish Macintyre]

I would like to use R to generate a histogram which has bars of variable bin
width with each bar having an equal number of counts. For example, if the
bin limits are the quartiles, each bar would represent 1/4 of the total
probability in the distribution.
An example of such an equal-probability histogram is presented by Nicholas
Cox at http://www.stata.com/support/faqs/graphics/histvary.html.
    
Thanks,
Hamish