Tolerates data values of duplicate or out of time points in OpenTSDB. (https://rbcommons.com/s/pepperdata/r/2832)
Previously, OpenTSDB throwed IllegalDataExceptions when the compaction process
observes multiple data values of the same time point. This change makes it leave
warning log messages instead and continue with one of the data points.  Also
fixes a bug that the metadata flag does not correctly reflect a new set of data
points from compaction.