add re-threading

It is possible that once in a while incoming or outgoing mail is added to the wrong thread. This can happen in two cases:

1) user error. A user posts a message in a wrong forum, or replies to an existing mail which is from a wrong thread

2) software error. it could happen that responses to a mail come in before the actual mail. In this case the responses will start new threads and these need to be moved below the right ones.

In both cases the approach is different.

In case 2) it is possible to achieve proper threads by simply looking at all the stored threading information. Nodes that have been created as new threads need to be copied to comments and the original node body needs to be changed to a redirector to the new comment.

In case 1) the admin will need to move comments or topics to either a different thread or create a new forum topic from them. Redirectors should also be added in place of the old comments/topics. In this case the stored threading info must be changed in order to accomodate this change and in case of rethreading based on 2) not make these changes undone. The UI will be a challenge which would be made much easier if this was to be a module for Drupal 4.7 with its superior form capabilities.