Use full buffering for streamrefs.

* libmailutils/stream/streamref.c (mu_streamref_create_abridged): Set
full buffering by default.

@@ -302,6 +302,9 @@ mu_streamref_create_abridged (mu_stream_t *pref, mu_stream_t str,
     off = start;
     off = start;
   sp->offset = off;
   sp->offset = off;
   *pref = (mu_stream_t) sp;
   *pref = (mu_stream_t) sp;
+
+  mu_stream_set_buffer (*pref, mu_buffer_full, 0);
+
   return 0;
   return 0;
 }
 }