I think this method and some of the code of `validateBinaryVersionsOnClasspath` should be merged with `setScalaLibraryError`. The logic is the same, setting the `classpathValid` flag and updating the markers if needed.
One difference is that 'normal' markers are deleted only if a Scala library error is detected. If a compatibility problem is detected, the build is stopped, but previous build markers are still visible.
I would go for something like: `def setScalaLibraryError(ListBuffer[(entry: IPath, severity: Int, message: String)])`