Use local protobuf when avaliable

[uis246]

[djdeath]

Protobuf might not always be available on the distro used, so I think it's much better to bundle our own version.

[uis246]

Not always, but when avaliable use system one, when either protobuf-c or protoc unavaliable - fallback to bundled protobuf

[djdeath]

But what's the advantage? I see more problems of compatibility to deal with.

[uis246]

Because system protobuf and bundled can conflict. Because when protobuf installed, gcc prefer headers of system one, but link with bundled.