Extend candidate index structure to keep track of multiple interval expressions per index. Each interval expression represents an equality prefix of query predicates to be pushed into an index scan. The system is currently limited to being able to encode a single equality prefix as an index scan. For example the predicates a=1, b=1, c=1, d > 5 form an equality prefix. In general we have 0+ equalities followed by 0 or 1 inequalities. This ticket is a prerequisite for RIN implementation.