Add support for OS-specific CA bundle locations

GitHub pull: #19
Suggested-by: Michael Vogt <mvo@ubuntu.com>
Signed-off-by: Eygene Ryabinkin <rea@codelabs.ru>

offlineimap/repository/IMAP.py

@@ -19,6 +19,7 @@ from offlineimap.repository.Base import BaseRepository
 from offlineimap import folder, imaputil, imapserver, OfflineImapError
 from offlineimap.folder.UIDMaps import MappedIMAPFolder
 from offlineimap.threadutil import ExitNotifyThread
+from offlineimap.utils.distro import get_os_sslcertfile
 from threading import Event
 import os
 from sys import exc_info
@@ -200,7 +201,7 @@ class IMAPRepository(BaseRepository):
 
     def getsslcacertfile(self):
         """Return the absolute path of the CA certfile to use, if any"""
-        cacertfile = self.getconf('sslcacertfile', None)
+        cacertfile = self.getconf('sslcacertfile', get_os_sslcertfile())
         if cacertfile is None:
             return None
         cacertfile = os.path.expanduser(cacertfile)