hadley/ggplot2 — pull request #1011 by BrianDiggs (2014-09-17 23:25:46+00:00)
Title: stat_function to compute function on data not aesthetic scale

`stat_function` currently computes the function with the transformed
(not original data) values. This causes the values to be wrong if
a different scale, other than continuous, is used.

See http://stackoverflow.com/q/9382032/892313 for an example
of this.