Dedupe should create indices for rules referring non-indexed columns

The dedupe rules shipped by default are referring columns that have indices, but if somebody creates a rule group with a rule referring a non-indexed column, the rule can be rather slow with larger databases (and can impact the users very much if that rule is used in profile creation, for example).

Upon rule group creation/alter, dedupe should check whether all of the referred column (or column pairs!) are indexed, and - if not - create the proper dedupe_* indices.