vendor id / vid keyword to give rulesets unique sid ranges
Since more and more rulesets are added to the rule index, risk of sid space collisions increase. It's been suggested that 'gid' should be used to separate them, but the gid field already has other uses in the real world.
So the idea is to add a 'vid' keyword to keep rulesets apart. The rule index should probably also be the master of the vid id's.