Minor: added regression tests for downTo.

Adopted tests from patch attached to KT-2586.

js/js.tests/test/org/jetbrains/k2js/test/semantics/RangeTest.java

@@ -53,4 +53,8 @@ public final class RangeTest extends SingleFileTranslationTest {
     public void testRangeEquals() throws Exception {
         checkFooBoxIsOk();
     }
+
+    public void testIntDownTo() throws Exception {
+        checkFooBoxIsOk();
+    }
 }

js/js.translator/testData/range/cases/intDownTo.kt

@@ -0,0 +1,24 @@
+package foo
+
+import java.util.ArrayList
+
+fun testDownTo() {
+    var elems = ArrayList<Int>()
+    for (i in 4 downTo 0) {
+        elems.add(i)
+    }
+    assertTrue(elems[0] == 4 && elems[1] == 3 && elems[2] == 2 && elems[3] == 1 &&  elems[4] == 0)
+}
+
+fun testDownToDoesNotIterate() {
+    for (i in 0 downTo 1) {
+        fail()
+    }
+}
+
+fun box(): String {
+    testDownTo()
+    testDownToDoesNotIterate()
+
+    return "OK"
+}