Update text for option

sql/mysqld.cc:
  Update of helptext for ndb-cache-check-time

sql/mysqld.cc

@@ -4647,7 +4647,7 @@ Disable with --skip-ndbcluster (will save memory).",
    (gptr*) &opt_ndb_optimized_node_selection,
    0, GET_BOOL, OPT_ARG, 1, 0, 0, 0, 0, 0},
   { "ndb-cache-check-time", OPT_NDB_CACHE_CHECK_TIME,
-    "A dedicated thread is created to update cached commit count value at the given interval.",
+    "A dedicated thread is created to, at the given millisecons interval, invalidate the query cache if another MySQL server in the cluster has changed the data in the database.",
     (gptr*) &opt_ndb_cache_check_time, (gptr*) &opt_ndb_cache_check_time, 0, GET_ULONG, REQUIRED_ARG,
     0, 0, LONG_TIMEOUT, 0, 1, 0},
 #endif