Merge pull request #190 in ZP/z-push from bugfix/ZP-871-integer-folderids-may-falsly-trigger to develop

* commit '0f10824f':
  ZP-871 Delete the pingable flag only if it is set, SyncCollections iterator: exclude 'false' as valid collection key (hierarchy state), explicitely implement SyncParameters->GetBackendFolderId() as it will return false in case of an upgraded profile.