Drop all connections when a sync failed

in accounts.sync() we would holdordropconnections() after each sync. But
depending on the repository configuration that might imply that
offlineimap tries to keep the same connections. But when a sync failed,
e.g. after a user had his computer suspended, it might be that our
connections that we have are worthless. So definitely drop them after a
failed sync.

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

Changelog.draft.rst

@@ -23,6 +23,9 @@ Changes
 Bug Fixes
 ---------
 
+* Drop connection if synchronisation failed. This is needed if resuming the
+  system from suspend mode gives a wrong connection.
+
 
 Pending for the next major release
 ==================================

offlineimap/accounts.py

@@ -268,7 +268,14 @@ class SyncableAccount(Account):
             mbnames.write()
             localrepos.forgetfolders()
             remoterepos.forgetfolders()
-        finally:
+        except:
+            #error while syncing. Drop all connections that we have, they
+            #might be bogus by now (e.g. after suspend)
+            localrepos.dropconnections()
+            remoterepos.dropconnections()
+            raise
+        else:
+            # sync went fine. Hold or drop depending on config
             localrepos.holdordropconnections()
             remoterepos.holdordropconnections()