ilist: Fix move-splice
ilist: Fix move-splice

Previously, this wasn't clearing the list that was being moved from.
This caused problems when the refcache's next list was spliced into
its re-review list because the objects would stay on the next list and
get freed a second time on the next round.

aclements/sv6,bowlofstew/sv6,aclements/sv6,aclements/sv6,bowlofstew/sv6,aclements/sv6,aclements/sv6,bowlofstew/sv6,bowlofstew/sv6,bowlofstew/sv6