Fix owdev builds

[pfrischmuth]

This branch contains a) some fixes such that no tests are failing anymore and b) changes such that the owdev jenkins builds are running again.

I tested the owdev build by temporary changing the branch... It seems to work again.

[white-gecko]

• [x] manual review commits
• [x] check unit tests: Tests: 647, Assertions: 1306, Incomplete: 3, Skipped: 1.
• [x] check integration tests mysql: Tests: 63, Assertions: 5834, Skipped: 7.
• [x] check integration tests virtuoso: Tests: 63, Assertions: 224, Skipped: 9.