storage/maria/trnman.c:
  Store min used trid in a global variable and change trnman_get_min_trid() to return this variable without using a mutex.
  This is safe as trnman_get_min_trid() is used for trid optimization and all algoritms will work even if it returns a slightly older trid.
  
  Also ensure that LOCK_trn_list is unlocked in trnman_new_trn() in the very unlikely case that lf_hash_get_pins() fails