### Improvements

- Updates Scala version to 2.10.7 for Java 9 support. [#3848][3848] by [@eed3si9n][@eed3si9n]

### Bug fixes

- Backports logging and `clean` concurrency fix. [#2156][2156]/[#3834][3834] by [@dwijnand][@dwijnand]
- Fixes over-compilation on Java 9 `scala.ext.dir`. [#3142][3142]/[#3701][3701] by [@retronym][@retronym]
- Fixes `addSbtPlugin` to use the correct version of sbt. [#3393][3393]/[#3397][3397] by [@dwijnand][@dwijnand]
- Changes the tuple enrichment deprecation warning messages. [#3455][3455] by [@olafurpg][@olafurpg]
- Fixes `addCompilerPlugin(...)` so it can consume compiler plugins published to Ivy repository using sbt 1.x. [#3784][3784]/[#3855][3855] by [@eed3si9n][@eed3si9n]

### Internal

- Fixes the source code to be `doc` friendly. [#3401][3401] by [@dwijnand][@dwijnand]


  [@eed3si9n]: https://github.com/eed3si9n
  [@dwijnand]: http://github.com/dwijnand
  [@cunei]: https://github.com/cunei
  [@jvican]: https://github.com/jvican
  [@Duhemm]: https://github.com/Duhemm
  [@olafurpg]: https://github.com/olafurpg
  [@retronym]: https://github.com/retronym
  [3401]: https://github.com/sbt/sbt/pull/3401
  [3393]: https://github.com/sbt/sbt/issues/3393
  [3397]: https://github.com/sbt/sbt/pull/3397
  [3455]: https://github.com/sbt/sbt/pull/3455
  [3142]: https://github.com/sbt/sbt/issues/3142
  [3701]: https://github.com/sbt/sbt/pull/3701
  [2156]: https://github.com/sbt/sbt/issues/2156
  [3834]: https://github.com/sbt/sbt/pull/3834
  [3848]: https://github.com/sbt/sbt/pull/3848
  [3784]: https://github.com/sbt/sbt/issues/3784
  [3855]: https://github.com/sbt/sbt/pull/3855