Use same code as provided in kernel. In first place
we used own prototypes in case of simplicity (they
all were based on "lock xadd" instruction. There is
no more need for that and we can switch to well known
kernel's api.

Because kernel uses plain int type to carry atomic
counters I had to add explicit u32 type for futexes,
as well as a couple of fixes for new api usage.
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>