Abstract R-version logic
Abstract R-version logic

Everything assumes we’re always downloading the latest version of R,
called `R-latest`. Thus, the only variable that needs to be changed to
make this Dockerfile work for R-devel versus stable R is `RBRANCH`,
since both `RBRANCH`es will always have a file called `R-latest` that
represents the latest daily version.

briandk/r-package-check