MB-8648: Adapt the spatial merger for the changes

Change-Id: If45cc878f46d967e32762905a21c4027f5d2ec16
Reviewed-on: http://review.couchbase.org/27553
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Filipe David Borba Manana <fdmanana@gmail.com>