code: func newMruInventoryMap(limit uint) *mruInventoryMap {
  	m := mruInventoryMap{
  		invMap:  make(map[wire.InvVect]*list.Element),
  		invList: list.New(),
  		limit:   limit,
  	}
  	return &m
  }
docs: // newMruInventoryMap returns a new inventory map that is limited to the number
  // of entries specified by limit.  When the number of entries exceeds the limit,
  // the oldest (least recently used) entry will be removed to make room for the
  // new entry.