Hypothetical perf improvements in DocValuesRangeQuery: reducing comparisons for some queries/segments [LUCENE-7618]

In reviewing the DocValuesRangeQuery code, it occured to me that there _might_ be some potential performance optimizations possible in a few cases relating queries that involve explicitly specified open ranges (ie: min or max are null) or in the case of SortedSet: range queries that are **effectively** open ended on particular segments, because the min/max are below/above the minOrd/maxOrd for the segment.

Since these seemed like semi-common situations (open ended range queries are fairly common in my experience, i'm not sure about the secondary SortedSet "ord" case, but it seemd potentially promising particularly for fields like incrementing ids, or timestamps, where values are added sequentially and likeley to be clustered together) I did a bit of experimenting and wanted to post my findings in jira – patch & details to follow in comments.

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Migrated from [LUCENE-7618](https://issues.apache.org/jira/browse/LUCENE-7618) by Chris M. Hostetter (@hossman), updated Jan 04 2017
Attachments: [LUCENE-7618.patch](https://apache.github.io/lucene-jira-archive/attachments/LUCENE-7618/LUCENE-7618.patch)

Start by reading DocValuesRangeQuery and the attached LUCENE-7618.patch, then review the issue's experimental findings about open ranges and segment bounds. Done means determining whether the proposed comparison reductions are valid and beneficial for the described query cases, with supporting details or measurements.

Written by the indexing model from the issue text.