Non-existent folder name in folder list

[Daniel Shahaf]

My setup is three accounts with autorefresh enabled.  In one of the
accounts I have a folderlist saying which folders should be synced, in
the other two I sync everything.  The folderlist also contains some
names which don't exist on the server-side.  (At least one of them never
existed on the server.)

I've upgraded from a recent tag (v6.3.2 or v6.3.3) to current master
(520e39d35536172d03b22d012cf4d8828687f2ff) this morning.

When I started offlineimap now it did not sync any folder in the first
account; it only printed a warning saying the server responded
"NO Mailbox does not exist".  (It did sync the other two accounts.)

Suggestions:

* Noisier failure.  If it fails to sync the account at all,
  <uppercase>I want to know about that</uppercase>.  One line saying
  only "WARNING" (not even "ERROR") in stdout isn't quite sufficient.

  (I had to revert to the default ui, btw, due to the Blinkenlights
  threadid bug mentioned in another thread.)

* Tolerance.  Sebastian suggests on IRC that the previous behaviour (of
  syncing the remaining folders in the account) should be restored.
  (and I concur)