refs codership/mysql-wsrep#201

- Fixes query cache so that it is aware of wsrep_sync_wait.
  Query cache would return (possibly stale) results to the
  client, regardless of the value of wsrep_sync_wait.
- Includes the test case that reproduced the issue.

sql/sql_class.h

@@ -2395,6 +2395,7 @@ public:
   size_t                    wsrep_TOI_pre_query_len;
   void*                     wsrep_apply_format;
   bool                      wsrep_apply_toi; /* applier processing in TOI */
+  wsrep_gtid_t              wsrep_sync_wait_gtid;
 #endif /* WITH_WSREP */
   /**
     Internal parser state.