Fixes and closes #4328.

No review.

git-svn-id: http://lampsvn.epfl.ch/svn-repos/scala/scala/trunk@24425 5e8d7ff9-d8ef-0310-90f0-a4852d11357a

src/library/scala/collection/parallel/ParIterableLike.scala

@@ -455,6 +455,18 @@ self =>
     executeAndWaitResult(new Max(ord, parallelIterator) mapResult { _.get }).asInstanceOf[T]
   }
   
+  override def maxBy[S](f: T => S)(implicit cmp: Ordering[S]): T = {
+    if (isEmpty) throw new UnsupportedOperationException("empty.maxBy")
+    
+    reduce((x, y) => if (cmp.gteq(f(x), f(y))) x else y)
+  }
+  
+  override def minBy[S](f: T => S)(implicit cmp: Ordering[S]): T = {
+    if (isEmpty) throw new UnsupportedOperationException("empty.maxBy")
+    
+    reduce((x, y) => if (cmp.lteq(f(x), f(y))) x else y)
+  }
+  
   override def map[S, That](f: T => S)(implicit bf: CanBuildFrom[Repr, S, That]): That = bf ifParallel { pbf =>
     executeAndWaitResult(new Map[S, That](f, pbf, parallelIterator) mapResult { _.result })
   } otherwise super.map(f)(bf)

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

@@ -28,7 +28,7 @@ import scala.collection.parallel.ParIterableIterator
  *  
  *  @author Aleksandar Prokopec
  *  @since 2.9
- *
+ *  
  *  @define Coll immutable.ParRange
  *  @define coll immutable parallel range
  */