NIL_REFERENCES: Added mechanism to cut (nil) references to marked classes (and their instances) during commit.
Check for nil_references.
Merge branch 'master-1.9' into matthias/nil-references-merged-with-master
Merge pull request #286 from MagLev/matthias/nil-references

NIL_REFERENCES: Added mechanism to cut (nil) references during commit
Merge branch 'master-1.9' into stefan/persisting-only-maglevrecord

Conflicts:
	src/kernel/bootstrap/Module.rb