Tried hard to save compile-time static type checking and make code
more readable, hiding native/compat details in macros.
I think, it's better now.

Also BTW fixes: #188 (and compatible zdtm test)
Signed-off-by: Dmitry Safonov <dsafonov@virtuozzo.com>
Reviewed-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>