Proxy prefetch cache becomes a command-line argument.

src/common/serve.h

@@ -154,8 +154,11 @@ int do_serve( struct server *, struct self_pipe * );
 struct mode_readwrite_params {
 	union mysockaddr     connect_to;
 	union mysockaddr     connect_from;
+
+	/* FIXME: these should be uint64_t and uint32_t respectively */
 	off64_t              from;
 	off64_t              len;
+
 	int                  data_fd;
 	int                  client;
 };