Support google/protobuf/compiler/plugin.proto

[yugui]

I would be great if this repository also contains a compiled version of google/protobuf/compiler/plugin.proto.

I expect that this repository contains the proto because it is a part of protoc distribution. So it should be common enough to store in this repository.

Currently I am using github.com/golang/protobuf/protoc-gen-go/plugin as a compiled version of the proto file but unfortunately that go package cannot coexist with google.golang.org/genproto/protobuf because both have their own instances of descriptor.proto and they collide with each other at runtime.

[pongad]

@yugui I'm sorry this flew under my radar. We overhauled the way .pb.go files in this repo are generated late last year. The coexistence problem should be solved now. Could you try again?

Due to the age of this issue, I'll close it for now. Please reopen if the problem persists.