POSIX requires that the RLIMIT_CPU resource limit that generates SIGXCPU be
counted on a per-process basis.  Currently, Linux implements this for
individual threads.  This patch fixes the semantics to conform with POSIX.

The essential machinery for the process CPU limit is is tied into the new
posix-timers code for process CPU clocks and timers.
Signed-off-by: Roland McGrath <roland@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>