MB-7624: extend copyright to include 2013

Change-Id: If43dff9ea9a34b85ccfcb68e762ca7d94645e31a
Reviewed-on: http://review.couchbase.org/24282
Reviewed-by: Philip Labee <philip@couchbase.com>
Tested-by: Philip Labee <philip@couchbase.com>