installer makes /dev/shm world writable even for root install

AS part of the post-install script /dev/shm is made world writable. Expanding rights on this for non root install is of course required but this should not be required for a root install.

For a non root install we can maybe document this since i think it'll be hard to automate a general purpose solution but a user could choose to setup a less restrictive group permission if this is of concern.