Protobuf seems to have an incompatible cmake every single release,
which makes including it with cmake itself stupid and indeed lead
to linking or even compile errors.
So, the point of not wanting to use protobuffers directly got again
proven in practice as its a messy thing in all regards.
This makes the unit test for our reimplementation of protobuf
parsing/building become optional. The unit test is the only one
that actually uses the protocol buffers stuff itself, as such
turning that off by default isolates our users from the mess it is.
tomFlowee
90c56b9caa