Git commits in Moodle 3.8.3 by Martin Gauk

commit b1345143ea81ce3a0b3a6b2ebaaa177fcdce2ba1
Author: Martin Gauk <gauk@math.tu-berlin.de>
Date:   Fri, 17 Jan 2020 20:13:41 +0800
Tag:    v3.8.3

MDL-51694 core_grades: use transactions when deleting