Update to libcouchbase 2.1.0

Change-Id: Ie1f046d6f04f188dae249c493f996159c2c0e16e
Reviewed-on: http://review.couchbase.org/28346
Tested-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Reviewed-by: Matt Ingenthron <matt@couchbase.com>