Hello. In Scala 2.10.0 M3 we're going to have manifests (but not class manifests) tied to the new Scala reflection mechanism.
At the moment, our implementation of Scala reflection requires scala-compiler.jar to be on the classpath of the classloader that loads scala-compiler.jar. We're planning to remedy this problem before the final release, but this is the best what we can do for now. Here's a thread that discusses the problem and tracks its status: http://groups.google.com/group/scala-internals/browse_thread/thread/2a531bebece6d66b.
If you're going to update the plugin for M3, please, take this peculiarity into account. If you need any help, drop me a line at any time.