Prevent annoying tooltip in Kotlin project

Module 'builtins' has no dependency on kotlin-runtime.jar, yet it has a lot of
Kotlin files. Add jet.Unit to the list of marker classes as an example of the
class not from the stdlib, but from built-ins. Since 'builtins' has jet.Unit in
its classpath, no tooltip is displayed

idea/src/org/jetbrains/jet/plugin/versions/KotlinRuntimeLibraryUtil.java

@@ -156,6 +156,8 @@ public class KotlinRuntimeLibraryUtil {
 
         ImmutableList<String> candidateClassNames = ImmutableList.of(
                 kotlinPackageClassFqName,
+                // For built-ins module in Kotlin project
+                "jet.Unit",
                 // For older versions
                 "kotlin.namespace",
                 // For really old versions