Allowing variable number of arguments in lf.op.and() and or().

This allows for much more readable syntax for the cases where 3+ clauses are
combined with an AND or OR predicate.
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Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=82482799
Fixing lovefield.min.js to include BaseBuilder#explain.

Fixed by adding @export annotation in BaseBuilder on all BaseBuilder methods
that come from the Builder interface.
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Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=82482920
Cleanup: Moving hr_schema testing related files under existing hr_schema folder.
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Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=82483004
Adding more perf regression tests (joins, index cost).

Specifically:
- Adding a new curve in existing SelectSingleRow graph, which
demonstrates current performance pain point in BTree#cost().
- Adding a new graph for joins with curves for theta-join and
equi-join accordingly.
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Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=82523214