Use AtomicMonotonic for ActiveStream::lastReadSeqno
Use AtomicMonotonic for ActiveStream::lastReadSeqno

The lastReadSeqno should never go backwards or repeat, so use
AtomicMonotonic to implement it to verify this.

Change-Id: Iec0074faac813d899311cd404d663fd26260eb91
Reviewed-on: http://review.couchbase.org/81281
Tested-by: Build Bot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>
Reviewed-by: Jim Walker <1cd02e31b43620d7c664e038ca42a060d61727b9@couchbase.com>

daverigby/kv_engine,daverigby/kv_engine,daverigby/kv_engine,daverigby/kv_engine