> set build.scala.versions 2.7.7
$ copy-file changes/P.scala project/build/P.scala
$ copy-file changes/A.scala a/src/main/scala/A.scala
$ copy-file changes/B.scala b/src/main/scala/B.scala
> reload

> project A
-> compile
> update
> compile

> project B
-> compile
> update
-> compile

$ touch b/declare.lib
> reload
-> compile
> update
> compile