[PATCH] sched: reduce task_struct size

more task_struct size reduction, by moving the debugging/instrumentation
fields to under CONFIG_SCHEDSTATS:

 (i386, nodebug):

                          size
                          ----
     pre-CFS              1328
         CFS              1472
         CFS+patch        1376

Signed-off-by: Ingo Molnar <mingo@elte.hu>