ZP-621 #comment added new SyncCollections state "HIERARCHY_CHANGED" which does not indicate an error and let Ping return SYNC_PINGSTATUS_FOLDERHIERSYNCREQUIRED as well in this case

git-svn-id: https://z-push.org/svn/z-push/trunk@1960 b7dd7b3b-3a3c-0410-9da9-bee62a6cc5b5