Rollup of bugfix releases for 5.1, 5.2 and 5.3 branches

Hi all,

We released (minor) bugfix releases 5.1.4, 5.2.1 and 5.3.1 for all current branches. Download as usual at https://www.domjudge.org/

These various fixes from the last few weeks, including: - Fix runguard reusing cpuacct cgroup potentially giving wrong runtimes. - Increase length of auditlog.action DB column, fixing SQL error when updating some configuration settings. - Fix testcase download filename. - Various small documentation fixes. - Fix display of user IP address on jury interface. - Fix automatic setting of clarification category in jury interface. - Delete team scoreboard cache data when deleting a team.

This also marks the end of life of the 5.1 branch. We recommend upgrading to either of the 5.2 or 5.3 branches.

Best, Jaap