MB-8780: added compaction option to avoid purging too new seqnos

Change-Id: I0dcdba09c276ca233add69446947e8f8906905fc
Reviewed-on: http://review.couchbase.org/28034
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Aaron Miller <apage43@ninjawhale.com>
Tested-by: Aaron Miller <apage43@ninjawhale.com>
Merge remote-tracking branch 'couchbase/2.1.1' into master

* couchbase/2.1.1:
  MB-8780: added compaction option to avoid purging too new seqnos

Change-Id: Ie0c6d3b579791ebae49f2037050e779db9518eda