Don't rely on protoc executable

[copumpkin]

It'd be nice for these projects to be as self-contained as possible, and relying on an environment protoc seems unfortunate when we're already explicitly depending on the protocol buffers maven package. I don't know if there's a clean way to generate source from a library, but a silent dependency makes me sad.

[gseitz]

Indeed, it's not ideal, far from it. Unfortunately, as far as I'm aware there's no Java API to generate the Java source. Maybe this protoc-jar project could be used for this purpose.

[copumpkin]

That seems perfect!

[gseitz]

@copumpkin: In case you're still using sbt-protobuf, I just published 0.4.0 with a new task runProtoc: TaskKey[Seq[String] => Int] which you can set to args => com.github.os72.protocjar.Protoc.runProtoc(args.toArray) to invoke the protobuf compiler coming from a downloaded dependent artifact (granted that the build has a dependency on the correct protoc-jar version).

[gseitz]

Fixed by 779c6ee.