Merge pull request #138 in ZP/z-push from bugfix/ZP-824-foldersync-should-cause-ping-to-force to develop

* commit 'd8718bdc':
  ZP-824 Remove local $sc as it is not needed.
  ZP-824 Invalidate all pingable flags on folders when doing a FolderSync (with changes) or FolderChange (Create, Update, Delete) operation.