wrong comments parent

After migration I've observed that nested comments behalf to an incorrect parent.

In the dada database, each comment has a rootid and a parentid. If both are equal, the objectid is refered to the parent article. If not equal, means the comment is nested. The rootid is the parent article and the parentid is the parent comment.

In any of those cases, the parentid is the only needed objectid. But if rootid != parentid, the parent is not an article but a comment. Dadamigrator does not take care of this.

Attached is a patch that fix this issue. It has been tested with success on my local imc.