Merge pull request scala#791 from axel22/issue/5336

Fix SI-5336.

Author: jsuereth

src/library/scala/collection/parallel/immutable/ParIterable.scala

@@ -34,6 +34,7 @@ extends collection/*.immutable*/.GenIterable[T]
    with collection.parallel.ParIterable[T]
    with GenericParTemplate[T, ParIterable]
    with ParIterableLike[T, ParIterable[T], collection.immutable.Iterable[T]]
+   with Immutable
 {
   override def companion: GenericCompanion[ParIterable] with GenericParCompanion[ParIterable] = ParIterable
 

src/library/scala/collection/parallel/mutable/ParIterable.scala

@@ -29,7 +29,8 @@ import scala.collection.GenIterable
 trait ParIterable[T] extends collection/*.mutable*/.GenIterable[T]
                         with collection.parallel.ParIterable[T]
                         with GenericParTemplate[T, ParIterable]
-                        with ParIterableLike[T, ParIterable[T], Iterable[T]] {
+                        with ParIterableLike[T, ParIterable[T], Iterable[T]]
+                        with Mutable {
   override def companion: GenericCompanion[ParIterable] with GenericParCompanion[ParIterable] = ParIterable
   //protected[this] override def newBuilder = ParIterable.newBuilder[T]