code: Index addIndex(int[] col, HsqlName name, boolean unique, boolean migrating, Expression predicate) {
          return addIndex(col, name, unique, migrating).withPredicate(predicate);
      }
docs: A VoltDB extended variant of addIndex that supports partial index predicate.
  
  @param col int[]
  @param name HsqlName
  @param unique boolean
  @param migrating is MIGRATING INDEX being created
  @param predicate Expression
  @return new index