Implemented workaround for SI-4789, no review.

git-svn-id: http://lampsvn.epfl.ch/svn-repos/scala/scala/trunk@25266 5e8d7ff9-d8ef-0310-90f0-a4852d11357a

src/library/scala/collection/generic/GenTraversableFactory.scala

@@ -38,9 +38,11 @@ abstract class GenTraversableFactory[CC[X] <: GenTraversable[X] with GenericTrav
   
   // A default implementation of GenericCanBuildFrom which can be cast
   // to whatever is desired.
-  private[collection] object ReusableCBF extends GenericCanBuildFrom[Nothing] {
+  private class ReusableCBF extends GenericCanBuildFrom[Nothing] {
     override def apply() = newBuilder[Nothing]
   }
+  // Working around SI-4789 by using a lazy val instead of an object.
+  lazy val ReusableCBF: GenericCanBuildFrom[Nothing] = new ReusableCBF
 
   /** A generic implementation of the `CanBuildFrom` trait, which forwards
    *  all calls to `apply(from)` to the `genericBuilder` method of