bug#31189: r-rcurl does not find CA bundle

[Ricardo Wurmus]

The r-rcurl package does not find a CA bundle and does not respect any
of the common environment variabls to set the location of the bundle.
This makes r-gprofiler (a user of r-rcurl) pretty useless as it cannot
access any of the online databases.

The fix here is to figure out where to inject a getenv call in case the
caller does not specify the “cainfo” argument.

--
Ricardo