Fix udev rules to support udev database content generated by older rules.

Fix udev rules to support udev database content generated by older rules.

This can happen with older rules (without support for synthesized events)
that are still part of initrd while using new udev rules in the system itself.

The consequence was that new udev rules incorrectly assumed that not having
DM_UDEV_PRIMARY_SOURCE_FLAG set always means the uevent is synthesized and
inappropriate (device is still not properly activated) and so it should be
ignored. However, initrd is not updated automatically while updating the
libdevmapper/udev rules in the system and so we end up with the rules not
detecting and setting crucial parts in the initrd environment and the rules
in the system that rely on the information that should have been stored in
udev db (which is incorrect in this configuration, of course).

The overall consequence is that the update of libdevmapper/lvm2 without
regenerating the initrd could end up with a boot failure! Ignoring the event
means removing any existing symlinks in /dev!

To fix this, increase udev rules version to make a difference. So from now on,
mark rules without proper support for synthesized events as
DM_UDEV_RULES_VSN="1" and 2 (or higher) if that support is included.