I think you should check if SVN has been installed correctly. Did you install SVN as a root user?
Try installing as a root, also check if it is installed in the correct location. To double check, try the command
svn help
This will help to check if svn has been installed. Post this step, install the psychtoolbox. If you think your path is corrupted, try created a temp user, install svn, install psychtoolbox.