Catch folderfilter errors in repository.IMAP.getfolders()

Rather than throwing ValueError, we now properly throw OfflineImapError
when selecting a folder in folderincludes. So we also need to catch
OfflineImapErrors here. If they are of severity FOLDER, just ignore the
invalid folder and continue. If the error is more severe, bubble it up.

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

Changelog.draft.rst

@@ -23,7 +23,9 @@ Changes
 Bug Fixes
 ---------
 
-
+* Selecting inexistent folders specified in folderincludes now throws
+  nice errors and continues to sync with all other folders rather than
+  exiting offlineimap with a traceback.
 
 Pending for the next major release
 ==================================

offlineimap/repository/IMAP.py

@@ -24,6 +24,7 @@ from threading import Event
 import re
 import types
 import os
+from sys import exc_info
 import netrc
 import errno
 
@@ -307,7 +308,12 @@ class IMAPRepository(BaseRepository):
                 for foldername in self.folderincludes:
                     try:
                         imapobj.select(foldername, readonly = 1)
-                    except ValueError:
+                    except OfflineImapError, e:
+                        # couldn't select this folderinclude, so ignore folder.
+                        if e.severity > OfflineImapError.ERROR.FOLDER:
+                            raise
+                        self.ui.error(e, exc_info()[2],
+                                      'Invalid folderinclude:')
                         continue
                     retval.append(self.getfoldertype()(self.imapserver,
                                                        foldername,