Certain MySQL went crazy after a failure
This time I have no idea what was real cause of the problem. The server froze and after restart MySQL refused to start at all.
The problem is quite well described at ticket http://bugs.mysql.com/bug.php?id=47134 . Makes me want to switch to MariaDB... tc.log, found from MySQL datadir, contained few bytes of binary data, so obviously corrupted. Removing the file made MySQL behave normally. Again, please bug me if everything is dying...