object_classes array is broken, again

The transforms patch seems to have forgotten to add
TransformRelationId to object_classes[], much like the RLS patch
forgot to add PolicyRelationId in the same place.

Fixing this is easy, but ISTM that we need to insert some sort of a
guard to prevent people from continuing to forget this, because it's
apparently quite easy to do.  Perhaps add_object_address should
Assert(OidIsValid(object_classes[oclass])), plus a (static?) assert
someplace checking that OidIsValid(object_classes[MAX_OCLASS - 1])?

-- 
Robert Haas
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