Fix make protoc

[orkunkl]

I fixed the bug that blocked #23.
In gogo/protobuf#601, @apelisse pointed me to the problems cause. It was spec/github.com/iov-one/weave/codec.proto.
Reason:

• includes field contains which import paths will be used when running protoc.
  • . means that import "x/custom/codec.go" will work inside this app (recommended to avoid GOPATH issues)
  • spec means that we can import "github.com/iov-one/weave/coins/codec.proto" and it will use the protobuf file from our spec directory (which must be kept up to date with the weave repo).
  • spec/github.com/iov-one/weave is needed as if we import eg. github.com/iov-one/weave/x/cash/codec.proto, it imports coins/codec.proto using relative imports to it's project. When we then import this via spec, the relative import doesn't work without this second line.

Everything seems okay until running make protoc. spec folder and spec/github.com/iov-one/weave folder includes weave package so the protoc generates these imports in x/custom/codec.pb.go:

import (
  github_com_iov_one_weave "github.com/iov-one/weave"
  weave "github.com/iov-one/weave"
)

The duality of github.com/iov-one/weave does not effect applications runtime but proto compiler gets confused. Solution is to add

option go_package = "github.com/iov-one/weave";

to spec/github.com/iov-one/weave/codec.proto. Now everything returned back to normal in protoc's aspect. Note: if you want to read more about option go_package here is an article.

If you have a better solution than Makefile, please let me know :)
Also thank you @apelisse :)

Resolves gogo/protobuf#601

[husio]

Great finding! How about adding it to weave instead of patching here?