Remove python<2.6 import workarounds (set & ssl)

'set' is builtin since python2.6, so remove the imports. Also 'ssl' exists
since 2.6 and has everything we need, so no need for conditional import
tests here anymore.

Signed-off-by: Sebastian Spaeth <Sebastian@SSpaeth.de>

offlineimap/folder/Base.py

@@ -23,10 +23,7 @@ import os.path
 import re
 from sys import exc_info
 import traceback
-try: # python 2.6 has set() built in
-    set
-except NameError:
-    from sets import Set as set
+
 
 class BaseFolder(object):
     def __init__(self, name, repository):