Correct build error from libcouchbase 2.3.1 update.

Change-Id: Icd707fbbc9b7cba50172699cb3be9e2b1c6f11f3
Reviewed-on: http://review.couchbase.org/36974
Tested-by: Brett Lawson <brett19@gmail.com>
Reviewed-by: Mark Nunberg <mnunberg@haskalah.org>
Reviewed-by: Brett Lawson <brett19@gmail.com>