Unit tests fail

Moodle 2 unit tests fail in a really big way. I will create subtasks for failures in particular areas.

It is general practice that software should not be released if any unit tests fail, so I marked this as 'blocker'.

As part of the OU's Moodle Monday (1 November) we will try to fix as many of these problems as we can (so everyone else, feel free to ignore them until after that date). Probably in the majority of cases the failures will be caused by test-rot rather than actual system failures, so we can fix them with low risk.