BUG#25712 - insert delayed and check table run together report
            crashed tables

Let MY_THREADSAFE have distinct value. Some functions call my_seek
passing MyFlags argument directly to it. This may cause unnecessary
locks, which may finally lead to a dead-lock (specifically see my_lock).


include/my_sys.h:
  Addition to fix for
  BUG#25712 - insert delayed and check table run together report
              crashed tables
  
  Let MY_THREADSAFE have distinct value. Some functions call my_seek
  passing MyFlags argument directly to it. This may cause unnecessary
  locks, which may finally lead to a dead-lock (specifically see my_lock).
  
  Also it doesn't affect my_pread/my_pwrite in any way. So the comment was
  updated.