Fix a handful of small one-time memory leaks in vbackup,

and one per-package memory leak (in writethread).

src/libventi/client.c

@@ -169,3 +169,12 @@ vtconnect(VtConn *z)
 	return 0;
 }
 
+int
+vtgoodbye(VtConn *z)
+{
+	VtFcall tx, rx;
+	
+	tx.msgtype = VtTgoodbye;
+	vtfcallrpc(z, &tx, &rx);	/* always fails: no VtRgoodbye */
+	return 0;
+}