Purpose of rules file:

This file re-assigns CD-ROM type devices to the "cdrom" group.


Description of rules:

There is only one rule here.  It depends on the 60-persistent-storage file,
though, because it requires the ID_TYPE environment variable to be set properly
for CD devices.  Normally the rules in the 60-persistent-storage.rules file
will run the correct *_id programs to do this properly.

If ID_TYPE is "cd", and this is a block device, and it's an add event, then we
assign the device to the "cdrom" group.  Simple, once the *_id programs have
all been run.