System connector predicate pushdown bug fix
Update to Hive 0.12
Add Null type to type registry
Implement HyperLogLog type and associated functions

Adds the following functions for manipulating HLLs:
- approx_set: aggregation function to create an HLL from varchar, bigint or double values
- merge: aggregation function to merge multiple HLLs
- cardinality: scalar function that computes the cardinality for an HLL
Rename HashJoinOperator => LookupJoinOperator
Rename JoinHash to LookupSource

This is preparation for adding index joins

Extract LookupSourceSupplier from HashSupplier
Rename HashSupplier to SettableLookupSupplier
Change position from int to long in LookupSource
Add support for index joins
Add unit tests for index joins