#436 Error handling for folder rename

[Alexandros Vellis]

There seems to be no error handling in STABLE for folder renaming, in function sqimap_mailbox_rename().

So, when a folder rename is happened, and the new name contains illegal characters, the error is not caught. The problem is that not only is the folder *NOT* renamed; it is also unsubscribed from! :-)

So here's a patch to add some basic error handling.

This contains a new translatable string: _("Error while renaming: %s") if there is a similar string, use that one instead.

This is not perfect, and all a user can do is press "Back", but it is much better now, since the original folder is not vanished from his view!

Alexandros

P.S. the diff might match with fuzzy line numbering, since I also had some other internal changes.

[Alexandros Vellis]