cleanup import statements and conform to PEP-8

Signed-off-by: Nicolas Sebrecht <nicolas.s-dev@laposte.net>

offlineimap/folder/Maildir.py

@@ -16,9 +16,11 @@
 #    along with this program; if not, write to the Free Software
 #    Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301 USA
 
-import os.path, os, re, time, socket
+import socket
+import time
+import re
+import os
 from Base import BaseFolder
-from offlineimap import imaputil
 from threading import Lock
 
 try: