allocated at startup).


storage/maria/ma_init.c:
  destroy transaction manager and log's pagecache when Maria shuts down
storage/maria/trnman.c:
  short_trid_to_active_trn!=NULL now serves to detect if
  trnman has initialized some objects and so if trnman_destroy()
  has objects to destroy. In other words, short_trid_to_active_trn
  serves as "trnman_inited" variable.
  trnman_destroy() is always called by maria_end(), but trnman_init() is
  not always called (for example in ma_test1), that's why
  trnman_destroy() cannot blindly destroy.