Added explicit option to generate the "generic service code" since by default protobuf 2.4.0 and later don't generate them. Also since protobuf 2.3.0 is the first version that understands this option, the minimum protobuf version required for Ostinato now becomes 2.3.0

common/protocol.proto

@@ -18,6 +18,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>
 */
 
 package OstProto;
+option cc_generic_services = true;
 
 message StreamId {
     required uint32 id = 1;