Do not use native CMake config for Protobuf on Linux (#1529)
Do not use native CMake config for Protobuf on Linux (#1529)

On Ubuntu 16.04, we have to install Protobuf 3. Unfortunately, `find_package()`ing Protobuf using native installed CMake `CONFIG` is problematic in case if there is a system Protobuf 2 installed, while the bundled CMake module works correctly and manages to avoid interference with system-installed Protobuf 2.
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