util.dbuffer: Add efficient shortcuts for discard() in certain cases If the buffer is already empty, nothing to do. If we're throwing away the whole buffer, we can just empty it and avoid read_chunk() (which in turn may collapse()). These shortcuts are much more efficient.

return {
  _all = {
  },
  default = {
    ["exclude-tags"] = "mod_bosh,storage,SLOW";
  };
  bosh = {
    tags = "mod_bosh";
  };
  storage = {
    tags = "storage";
  };
}