Remove "Iterator.iterator()" intrinsic, add stdlib function

libraries/stdlib/src/kotlin/Iterators.kt

@@ -4,6 +4,11 @@ import kotlin.support.*
 import java.util.Collections
 import kotlin.test.assertTrue
 
+/**
+ * Returns the given iterator itself. This allows to use an instance of iterator in a ranged for-loop
+ */
+public fun <T> Iterator<T>.iterator(): Iterator<T> = this
+
 /**
  * Returns an iterator which invokes the function to calculate the next value on each iteration until the function returns *null*
  */