Add a pair of rlimits for allowing non-root tasks to raise nice and rt
priorities. Defaults to traditional behavior. Originally written by
Chris Wright.

The patch implements a simple rlimit ceiling for the RT (and nice) priorities
a task can set.  The rlimit defaults to 0, meaning no change in behavior by
default.  A value of 50 means RT priority levels 1-50 are allowed.  A value of
100 means all 99 privilege levels from 1 to 99 are allowed.  CAP_SYS_NICE is
blanket permission.

(akpm: see http://www.uwsg.iu.edu/hypermail/linux/kernel/0503.1/1921.html for
tips on integrating this with PAM).

Signed-off-by: Matt Mackall <mpm@selenic.com>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>