protobuf: Start switching our image entries to Google's protobuf

A short story -- there were a long conversation on which format should
be used to keep checkpointed data on disk image. We ended up in using
Google's Protocol Buffers (see https://developers.google.com/protocol-buffers/
for detailed description). Thus image entries should be convered to PB.

This patch converts fdinfo_entry to PB "message fdinfo_entry".

Build note: one should have protobuf and protobuf-c installed to be able
to build crtools.

 - http://code.google.com/p/protobuf/
 - http://code.google.com/p/protobuf-c/

Inspired-by: Pavel Emelianov <xemul@parallels.com>
Inspired-by: Kinsbursky Stanislav <skinsbursky@openvz.org>
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

include/image.h

@@ -131,13 +131,6 @@ struct inotify_file_entry {
 	fown_t	fown;
 } __packed;
 
-struct fdinfo_entry {
-	u32	fd;
-	u8	type;
-	u8	flags;
-	u32	id;
-} __packed;
-
 struct fs_entry {
 	u32	cwd_id;
 	u32	root_id;