headers: Unify include guards (in comments) and a few fixes

 - fix names in comments
 - add empty lines where needed
 - fix rbtree.h
 - fix syscall-types.h

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>