Products-zcatalog

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- Refactored value index logic. Determine value indexes per catalog instead of
globally. Store value index set in the priority map, so it can be seen in the
ZMI and stored in the module level storage.

- Added support for using ZCatalog as local utility.
This feature requires the optional `five.globalrequest` dependency.

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- Fixed incorrect calculation of batches in the second half of the result set
in sortResults.

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- Increase plan precision to 4 digits in its string representation.

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- In the string representation of a catalog plan, round the times to at most
two digits after the comma.

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- Put back the `weightedIntersection` optimization but guard against results
with values and do the appropriate fallback to the weighted version.

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- Restored preserving score values from ZCTextIndex indices.
https://bugs.launchpad.net/zope2/+bug/815469