Add HashSet to stdlib

Author: odersky

tests/pos-special/stdlib/collection/Iterator.scala

@@ -562,7 +562,7 @@ trait Iterator[+A] extends IterableOnce[A] with IterableOnceOps[A, Iterator, Ite
     */
   def distinctBy[B](f: A -> B): Iterator[A]^{this} = new AbstractIterator[A] {
 
-    private[this] val traversedValues = mutable.HashSet.empty[B]
+    private[this] val traversedValues = mutable.HashSet.empty[B @uncheckedCaptures]
     private[this] var nextElementDefined: Boolean = false
     private[this] var nextElement: A = _
 

tests/pos-special/stdlib/collection/StrictOptimizedSeqOps.scala

@@ -25,7 +25,7 @@ trait StrictOptimizedSeqOps [+A, +CC[_], +C]
 
   override def distinctBy[B](f: A -> B): C = {
     val builder = newSpecificBuilder
-    val seen = mutable.HashSet.empty[B]
+    val seen = mutable.HashSet.empty[B @uncheckedCaptures]
     val it = this.iterator
     while (it.hasNext) {
       val next = it.next()