Fix foldRight implementation for iterables

libraries/stdlib/test/CollectionTest.kt

@@ -195,13 +195,27 @@ class CollectionTest {
         }
     }
 
+    test fun foldWithNonCommutativeOperation() {
+        expect(1) {
+            val numbers = arrayList(1, 2, 3)
+            numbers.fold(7) {a, b -> a - b}
+        }
+    }
+
     test fun foldRight() {
-        expect("4321") {
+        expect("1234") {
             val numbers = arrayList(1, 2, 3, 4)
             numbers.map<Int, String>{it.toString()}.foldRight(""){ a, b -> a + b}
         }
     }
 
+    test fun foldRightWithNonCommutativeOperation() {
+        expect(-5) {
+            val numbers = arrayList(1, 2, 3)
+            numbers.foldRight(7) {a, b -> a - b}
+        }
+    }
+
     test fun groupBy() {
         val words = arrayList("a", "ab", "abc", "def", "abcd")
         val byLength = words.groupBy{ it.length }