No need to walk up the directories if we need
to include protobuf file. This was always a bad
use of ability to walk the filesystem from other
headers.

Same time we don't need -I$(SRC_DIR)/protobuf/
in general makefile anymore.

[xemul: Small fixlet in head Makefile, since patch
 it out-of-order]
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>