[PATCH] RLIMIT_CPU: document wrong return value

Document the fact that setrlimit(RLIMIT_CPU) doesn't return error codes when
it should.  I don't think we can fix this without a 2.7.x..

Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Ulrich Weigand <uweigand@de.ibm.com>
Cc: Cliff Wickman <cpw@sgi.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>