There were so many changes into mtr (this is the new mtr coming) that I rather
copied mtr from 6.0-main here (at least this one knows how to run Maria tests).
I also fixed suite/maria tests to be accepted by the new mtr.
mysys/thr_mutex.c:
adding DBUG_PRINT here, so that we can locate where the warning is issued.
(BUG#41127: Maria: assertion when SHOW ENGINE MARIA LOGS and missing logs)
mysql-test/suite/maria/r/maria_showlog_error.result:
test suite for the BUG#41127
mysql-test/suite/maria/t/maria_showlog_error.test:
test suite for the BUG#41127
storage/maria/ha_maria.cc:
Do not use MY_WME in the stat call which errors we process on high level.