Relevant updates hidden after behaviour change in 0.2.0 w.r.t. crossScalaVersions

[barnardb]

The behaviour change in 0.2.0 has a number of downsides for me. My projects that target multiple versions often use different library versions with different Scala versions. Using sbt-updates versions before 0.2.0 I typically run sbt +crossScalaVersions to get a per-Scala-version update report. The new behaviour hides relevant updates from me.

For example, there are no versions of Akka prior to 2.4 released for Scala 2.12, but beginning with Akka 2.4 they stopped building for Scala 2.10. So a project targeting 2.10, 2.11 and 2.12 has to use different versions of Akka for 2.10 and 2.12. With the current logic, I won't any updates for Akka, because they will never release a version for all of those Scala versions.

I also see this with the org.scala-lang.modules libraries such as scala-xml and scala-parser-combinators that were split out of the Scala standard library in Scala 2.12. Projects that use these libraries need to depend on these artifacts for 2.11 and 2.12, but not for 2.10. With the new logic I don't see updates for these libraries, because they aren't released for 2.10.

One possibility for addressing this would be to make an option that enables the old behaviour.

[rtimush]

crossScalaVersions support was introduced in response to #44, so both the old and the new behaviors are useful in some scenarios. It seems that the only option is to introduce a configuration parameter to let the build author control whether he wants to use different dependency versions for different Scala versions or not.