[PATCH] Make RLIMIT_NICE ranges consistent with getpriority(2)

As suggested by Michael Kerrisk <[e-mail]>, make RLIMIT_NICE
consistent with getpriority before it becomes available in released glibc.

Signed-off-by: Matt Mackall <[e-mail]>
Acked-by: Ingo Molnar <[e-mail]>
Acked-by: Chris Wright <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

kernel/sched.c

···
  */
 int can_nice(const task_t *p, const int nice)
 {
-	/* convert nice value [19,-20] to rlimit style value [0,39] */
-	int nice_rlim = 19 - nice;
+	/* convert nice value [19,-20] to rlimit style value [1,40] */
+	int nice_rlim = 20 - nice;
 	return (nice_rlim <= p->signal->rlim[RLIMIT_NICE].rlim_cur ||
 		capable(CAP_SYS_NICE));
 }