0548f696795b accidentally changed the behavior of cgpacker._close().
The old behavior moved _nextclrevtolocalrev to _clrevtolocalrev only
when _nextclrevtolocalrev was present and then removed
_nextclrevtolocalrev. The bad behavior performed this move
then cleared _clrevtolocalrev because it was the same object as
_nextclrevtolocalrev.
This commit restores the previous behavior.
Surprisingly, no tests changed as a result of this bad logic. I'm
not sure why.