validate_params?

[tdhock]

we need to specify non-standard geom params such as geom_point(chunk_vars=c("var1", "var2"))

@faizan-khan-iit implemented a PR https://github.com/hadley/ggplot2/pull/1649 which was rejected by ggplot2.

now we have to wait until ggplot2 figures out a solution to the issue https://github.com/hadley/ggplot2/issues/1585

until then, I suggest we continue to depend on Faizan's validate_params branch https://github.com/faizan-khan-iit/ggplot2/tree/validate-params