IMAP, Maildir, and LocalStatus abort if in dry-run mode. IMAP and Maildir
will log that they "would have" created a new folder.
This will probably fail later on as we can not cache messagelists on
folder that don't exist, so --dry-run is not yet safe when new folders
have been created.
Signed-off-by: Sebastian Spaeth <Sebastian@SSpaeth.de>