dart.install failing when overwriting an existing installation in a different location

all is in the title, it seems impossible to overwrite the installation with the same version but in a different place.

Here is the workflow that fails:

1. install a new version of DART with ptd.dart.install
2. try to install in another location: fails suggesting to set overwrite=True, but still keeps the created directories.
3. try to install in another location with overwrite=True: fails because the directories already exist (although they shouldn't)

The workaround is to remove both the original ~/.dartrcxxx file as well as the created directories that are empty.

This workflow should be possible without manual intervention:

1. remove the newly created directories when install fails
2. just move the original installation to the new location (or simply remove it keeping the user_data) and adapt the ~/.dartrcxxx file
3. create an uninstall function, to be able to uninstall (i.e. completely remove) an existing installation.