ENG-4306 Make VoltTableUtil.CSV_NULL public for use by client programmers.
ENG-4306 Expose CSV_NULL constants through VoltTable re: review feedback r=nshi,r=jhugg
Merge branch 'master' into ENG-4306-CSV_NULL
Merge pull request #388 from VoltDB/ENG-4306-CSV_NULL

ENG-4306 Make VoltTableUtil.CSV_NULL public for use by client programmers.