Make rio.c comment 80-columns friendly.

src/rio.h

@@ -43,10 +43,11 @@ struct _rio {
     size_t (*read)(struct _rio *, void *buf, size_t len);
     size_t (*write)(struct _rio *, const void *buf, size_t len);
     off_t (*tell)(struct _rio *);
-    /* The update_cksum method if not NULL is used to compute the checksum of all the
-     * data that was read or written so far. The method should be designed so that
-     * can be called with the current checksum, and the buf and len fields pointing
-     * to the new block of data to add to the checksum computation. */
+    /* The update_cksum method if not NULL is used to compute the checksum of
+     * all the data that was read or written so far. The method should be
+     * designed so that can be called with the current checksum, and the buf
+     * and len fields pointing to the new block of data to add to the checksum
+     * computation. */
     void (*update_cksum)(struct _rio *, const void *buf, size_t len);
 
     /* The current checksum */