> publish
$ delete A.scala build.sbt

$ mkdir ext
$ copy-file changes/A.scala ext/A.scala
$ copy-file changes/B.scala B.scala
$ copy-file changes/Build.scala project/Build.scala
$ copy-file changes/ext.sbt ext/build.sbt

-> compile

$ touch binary
> reload
> run 3

$ delete binary
$ touch source
> reload
> run 5

$ touch binary source
> reload
> run 5

$ touch ext/older
> reload
> run 5