Make IterableLike.toIterator more efficient

Override TraversableLike.toIterator which uses unnecessary toStream.

Fixes SI-4802.  Contributed by Yang Zhang.

git-svn-id: http://lampsvn.epfl.ch/svn-repos/scala/scala/trunk@25302 5e8d7ff9-d8ef-0310-90f0-a4852d11357a

src/library/scala/collection/IterableLike.scala

@@ -85,6 +85,8 @@ self =>
     iterator.reduceRight(op)
   override /*TraversableLike*/ def toIterable: Iterable[A] = 
     thisCollection
+  override /*TraversableLike*/ def toIterator: Iterator[A] =
+    iterator
   override /*TraversableLike*/ def head: A =
     iterator.next