To not bloat util.h or image.h the protobuf.h introduced to handle all PB needs.

We represent our PB objects as pairs of records

  | 4 bytes for object packed size
  +---
  | X bytes -- object itself

v3:
 - Use plain read/write calls
 - Use local buffers for small objects

v4:
 - Add pb_pksize helper to calculate object
   size with header
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>