Previously when we've been on early stage we
tried to workaround lack of prlimit libc call
simply providing own implementation,  but it
cause problems on some libc configurations so
simply use rlimit64 and __NR_prlimit64 syscall
directly.

The kernel must support __NR_prlimit64 syscall
and provide rlimit64 structure as well.
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>