#663 Mails lost when moving subfolder

[Martin Petříček]

How to reproduce:

1. Folder-> New subfolder
2. Pick Inbox as parent folder, type in any name and
change type to MBOXFolder. Click OK
3. Via Drag and drop, drag the newly created folder from
Inbox to "Local Folders" (one level up)

The folder now looks unconnected. Until restart all
further folder you create don't show themselves in folder
list, after restarting columba, the folder you initially
moved is now empty (there still is one file in the
directory where data for folder are located with all the
messages, but you have to move it out and import its
content somewhat manually as it is not exactly in unix
mailbox format (but sed can solve it) ... less experienced
users will probably lose the data completely ...)