Implement ui.makefolder and abort repo.makefolder() in dry-run mode

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>

offlineimap/repository/Maildir.py

@@ -81,7 +81,9 @@ class MaildirRepository(BaseRepository):
             levels will be created if they do not exist yet. 'cur',
             'tmp', and 'new' subfolders will be created in the maildir.
         """
-        self.debug("makefolder called with arg '%s'" % (foldername))
+        self.ui.makefolder(self, foldername)
+        if self.account.dryrun:
+            return
         full_path = os.path.abspath(os.path.join(self.root, foldername))
     
         # sanity tests