Feature request: check for multiple .Renviron files and throw a warning if found

[jmb01]

It has been noted (e.g., here) that on Windows it is possible for R and RStudio to check for .Renviron in different places, causing confusion when changes are made via edit_r_environ() and then don't take effect upon restart.

It would be helpful to check for the presence of .Renviron in both locations and to throw a warning if a version is found in a location other than the one being edited.