Scenario of the BUG#40731 ("Maria: hang (probably in page cache) under concurrency"):
      T1: Disable logging for the table
      T1: Start inserting into the table
      T2: Tries to lock the table so waits.
      T2: Tries unlock and relock during the process see that the table has disabled logging and reenables it
      T1: Got DBUG_ASSERT because suddenly start use table with transaction switched on which is not expected during bulk insert

storage/maria/ma_pagecache.c:
  Page type print added for debugging purposes.
storage/maria/ma_recovery.c:
  Check that it was this thred which switched off logging (transactional mode).
storage/maria/maria_def.h:
  Flag for controling which thread switched off transactiona mode for the table added.