MB-7532 Set the default value of a rev sequence num to 1.

As the XDCR always expects a positive value for a revision
sequence number, its default value should be initialized to 1.

Change-Id: I7a281ad55d9c5d7e4ed93a6d4e33c609606f7f29
Reviewed-on: http://review.couchbase.org/23964
Reviewed-by: Michael Wiederhold <mike@couchbase.com>
Reviewed-by: Jin Lim <jin@couchbase.com>
Tested-by: Chiyoung Seo <chiyoung.seo@gmail.com>
Reviewed-on: http://review.couchbase.org/24002
MB-7543 Rev sequence number shouldn't be set to zero.

We should make sure that the revision sequence number shouldn't
be zero during warmup or when we receive tap_deletion,
tap_mutation, set_with_meta, and delete_with_meta.

Change-Id: I3316e0b688e2f29efc94533fab6fe61df0ea871a
Reviewed-on: http://review.couchbase.org/24004
Reviewed-by: Jin Lim <jin@couchbase.com>
Tested-by: Chiyoung Seo <chiyoung.seo@gmail.com>