OK, so after some checking with @skyluc :

- the dependency  on scala-xml is only from scaladoc, so the resolve:optional is pertinent
- the dependency on scala-parser-combinators is non-existent, the poms should be cleaned
- `test/disabled/presentation/akka/src/akka/config/ConfigParser.scala` should go away or be refactored to avoid the dependency on combinators

practical consequences for this PR:
- strict versioning (`[===, ===]`) AND `resolution:= optional` for scala -xml seems the best option
- you can remove the scala-parser-combinators dependency

/cc @phaller with whom I talked about this