Fix run/t3569.scala under checkinit
Fix run/t5256h.scala under checkinit
SI-8570 set the checkinit bit for unit-typed fields of traits

Fix only, refactoring in subsequent commit.
Clarify and clean up trait getter / setter generation
Disable run/t7974 under checkinit
Merge pull request #3730 from lrytz/checkinit

Fix checkinit build