hadley/ggplot2 — pull request #970 by baptiste (2014-06-02 23:34:55+00:00)
Title: check.class argument to ggsave

optional by-pass of ggsave checks that an object of class ggplot is being recorded.
In addition, a grid.draw method is defined, rather than calling print()
directly, to allow other grobs such as modified gtables to be saved.