Play backward compatibility issue

I've just tried using `1.0.0-M1` with Play and unfortunately it is not possible.

The first thing I've come across is that some APIs have become private e.g.:

https://github.com/sbt/sbt-native-packager/blob/master/src/main/scala/com/typesafe/sbt/packager/archetypes/JavaApp.scala#L111

Play actually uses the `makeJarName` function (there may be others, but I've not been able to progress beyond this issue so far).

I'm just wondering if we should re-visit what was made private - how concerned are we re. backward compatibility from an API perspective?