Re-scan list of remote folders on each sync

rather than just up-front.

fixes deb#396772

offlineimap/accounts.py

@@ -146,6 +146,8 @@ class AccountSynchronizationMixin:
                 folderthreads.append(thread)
             threadutil.threadsreset(folderthreads)
             mbnames.write()
+            localrepos.forgetfolders()
+            remoterepos.forgetfolders()
             localrepos.holdordropconnections()
             remoterepos.holdordropconnections()
         finally:

offlineimap/repository/Base.py

@@ -106,6 +106,11 @@ class BaseRepository(CustomConfig.ConfigHelperMixin):
         """Returns a list of ALL folders on this server."""
         return []
 
+    def forgetfolders(self):
+        """Forgets the cached list of folders, if any.  Useful to run
+        after a sync run."""
+        pass
+
     def getsep(self):
         raise NotImplementedError
 

offlineimap/repository/IMAP.py

@@ -160,6 +160,9 @@ class IMAPRepository(BaseRepository):
         imapobj = self.imapserver.acquireconnection()
         self.imapserver.releaseconnection(imapobj)
 
+    def forgetfolders(self):
+        self.folders = None
+
     def getfolders(self):
         if self.folders != None:
             return self.folders