Name the protocol version types

This makes the code clearer, and will help us replace them with proper
structs and get rid of the macros later.

src/libstore/remote-store-connection.hh

@@ -30,7 +30,7 @@ struct RemoteStore::Connection
      * sides support. (If the maximum doesn't exist, we would fail to
      * establish a connection and produce a value of this type.)
      */
-    unsigned int daemonVersion;
+    WorkerProto::Version daemonVersion;
 
     /**
      * Whether the remote side trusts us or not.