Add sql optimization for group by partition column,get rid of reAggregation on coordinator
Fix the related tests
Renaming most of the variables with 'm_' prefix
Add more planner negative tests
Merge branch 'master' of github.com:VoltDB/voltdb into ENG-6297-groupby-pk-opt
Merge pull request #1389 from VoltDB/ENG-6297-groupby-pk-opt

Eng 6297 groupby pk opt