I71 - lookup R versions on HPC portal

[weshinsley]

This seems to work for me locally - although I am getting a range of strange test failures in other places.
Update: 4 test failures on Win fixed, and a further 3 are skipped on windows. See https://vimc.myjetbrains.com/youtrack/issue/mrc-483 for the skipped ones.

[richfitz]

I don't think this will work in the installed package. Typically we do this with a package environment so something like

cache <- new.env(parent.env = emptyenv())

then assigning into that

if (is.null(cache$r_versions) || refresh) {
   ...
   cache$r_versions <- whatever
}

I don't think we need the time-based caching here - once per session should be ample

[weshinsley]

Done!