py3: raise exceptions using six module

There is no other way to make Python2 and Python3 happy, because syntax
raise E, V, T is incompatible with the latter.

Signed-off-by: Łukasz Żarnowiecki <dolohow@outlook.com>
Signed-off-by: Nicolas Sebrecht <nicolas.s-dev@laposte.net>

offlineimap/repository/__init__.py

@@ -17,6 +17,8 @@
 
 from sys import exc_info
 
+import six
+
 try:
     from configparser import NoSectionError
 except ImportError: #python2
@@ -68,16 +70,14 @@ class Repository(object):
         except NoSectionError as e:
             errstr = ("Could not find section '%s' in configuration. Required "
                       "for account '%s'." % ('Repository %s' % name, account))
-            raise OfflineImapError(errstr, OfflineImapError.ERROR.REPO), \
-                None, exc_info()[2]
+            six.reraise(OfflineImapError(errstr, OfflineImapError.ERROR.REPO), None, exc_info()[2])
 
         try:
             repo = typemap[repostype]
         except KeyError:
             errstr = "'%s' repository not supported for '%s' repositories."% \
                 (repostype, reqtype)
-            raise OfflineImapError(errstr, OfflineImapError.ERROR.REPO), \
-                None, exc_info()[2]
+            six.reraise(OfflineImapError(errstr, OfflineImapError.ERROR.REPO), None, exc_info()[2])
 
         return repo(name, account)