Update to match semantics of new imaplib2

The biggest change here is that imapobj.untagged_responses is no
longer a dictionary, but a list. To access it, I use the semi-private
_get_untagged_response method.

* offlineimap/folder/IMAP.py (IMAPFolder.quickchanged,
  IMAPFolder.cachemessagelist): imaplib2 now explicitly removes its
  EXISTS response on select(), so instead we use the return values from
  select() to get the number of messages.

* offlineimap/imapserver.py (UsefulIMAPMixIn.select): imaplib2 now
  stores untagged_responses for different mailboxes, which confuses us
  because it seems like our mailboxes are "still" in read-only mode when
  we just re-opened them.  Additionally, we have to return the value
  from imaplib2's select() so that the above thing works.

* offlineimap/imapserver.py (UsefulIMAPMixIn._mesg): imaplib2 now
  calls _mesg with the name of a thread, so we display this
  information in debug output. This requires a corresponding change to
  imaplibutil.new_mesg.

* offlineimap/imaplibutil.py: We override IMAP4_SSL.open, whose
  default arguments have changed, so update the default arguments. We
  also subclass imaplib.IMAP4 in a few different places, which now
  relies on having a read_fd file descriptor to poll on.

Signed-off-by: Ethan Glasser-Camp <ethan@betacantrips.com>
Signed-off-by: Nicolas Sebrecht <nicolas.s-dev@laposte.net>

offlineimap/imapserver.py

@@ -48,6 +48,8 @@ class UsefulIMAPMixIn:
            and self.is_readonly == readonly:
             # No change; return.
             return
+        # Wipe out all old responses, to maintain semantics with old imaplib2
+        del self.untagged_responses[:]
         result = self.__class__.__bases__[1].select(self, mailbox, readonly)
         if result[0] != 'OK':
             raise ValueError, "Error from select: %s" % str(result)
@@ -55,9 +57,10 @@ class UsefulIMAPMixIn:
             self.selectedfolder = mailbox
         else:
             self.selectedfolder = None
+        return result
 
-    def _mesg(self, s, secs=None):
-        imaplibutil.new_mesg(self, s, secs)
+    def _mesg(self, s, tn=None, secs=None):
+        imaplibutil.new_mesg(self, s, tn, secs)
 
 class UsefulIMAP4(UsefulIMAPMixIn, imaplibutil.WrappedIMAP4):
     # This is a hack around Darwin's implementation of realloc() (which