eo ptr ind: pack memory, use in mmap fifo as recycle trash

eo ptr ind: pack memory, use in mmap fifo as recycle trash

  - pack active flag and generation nbr in an _Eo_Id_Entry struct
  - replace Eina_Trash with a fifo which lives in mmaped memory owned by eo_id.
  - fifo uses indexes instead of pointers to spare memory
  - never used entries are served first, then those in the fifo
    are reused, thus we ensure that a freed entry won't soon be reused.