Make innodb_thread_concurrency 0 by default, and extend

 the usable range to 0..1000 (0 disables the thread throttling).


sql/mysqld.cc:
  innodb_thread_concurrency is 0..1000 now, and
   0 (the default) disables the thread throttling.

sql/mysqld.cc

@@ -5899,9 +5899,11 @@ log and this option does nothing anymore.",
    (gptr*) &srv_n_spin_wait_rounds,
    0, GET_LONG, REQUIRED_ARG, 20L, 0L, ~0L, 0, 1L, 0},
   {"innodb_thread_concurrency", OPT_INNODB_THREAD_CONCURRENCY,
-   "Helps in performance tuning in heavily concurrent environments.",
+   "Helps in performance tuning in heavily concurrent environments. "
+   "Sets the maximum number of threads allowed inside InnoDB. Value 0"
+   " will disable the thread throttling.",
    (gptr*) &srv_thread_concurrency, (gptr*) &srv_thread_concurrency,
-   0, GET_LONG, REQUIRED_ARG, 8, 1, 1000, 0, 1, 0},
+   0, GET_LONG, REQUIRED_ARG, 8, 0, 1000, 0, 1, 0},
   {"innodb_thread_sleep_delay", OPT_INNODB_THREAD_SLEEP_DELAY,
    "Time of innodb thread sleeping before joining InnoDB queue (usec). Value 0"
     " disable a sleep",