Use dedicated branches for memcached for 3.0 and 3.0.1

Change-Id: I1c002a3ff193d4ff75372dd962dc6a87f9431cff
Reviewed-on: http://review.couchbase.org/38551
Reviewed-by: Chris Hillery <ceej@couchbase.com>
Tested-by: Chris Hillery <ceej@couchbase.com>