Incorrect installation when R installation is cancelled

Hi again,

if you cancel R installation then installer by default proceeds further and fails to launch the app, even if you do have R already installed (in a different, compatible version). In the latter case the paths are not set correctly. There is no "cancel" nor "back" button in the step following the R installer, nor an automatic rollback/cancellation.

Best possibly would be to attempt to detect another, newer version of R (as a step torwards #24 ), and only if not found auto-rollback/cancel the installer. Independently, a "cancel" button in each step would make sense.

Best,
Mik