If comments were moved because an object on a higher level than the
commented object was moved, these comments were wrongly reindexed.
The commented object also got a wrong __parent__ pointer.
This fixes https://dev.plone.org/ticket/13172.
If the comment tree had just one top level comment the whole tree was
removed by the JS code if just one comment in the tree was deleted.
These comments were (correctly) not removed from the ZODB.