KT-3823 Standard sort function requires MutableIterable by no reason

#KT-3823 Fixed

libraries/stdlib/src/kotlin/IterablesSpecial.kt

@@ -64,7 +64,7 @@ public fun <T> Iterable<T>.containsItem(item : T) : Boolean {
 }
 
 
-public inline fun <T: Comparable<T>> MutableIterable<T>.sort() : List<T> {
+public inline fun <T: Comparable<T>> Iterable<T>.sort() : List<T> {
     val list = toCollection(ArrayList<T>())
     java.util.Collections.sort(list)
     return list

libraries/stdlib/test/CollectionTest.kt

@@ -402,6 +402,18 @@ class CollectionTest {
         //    assertFalse(IterableWrapper(linkedList<Int>()).contains(15))
     }
 
+    test fun sortForMutableIterable() {
+        val list : MutableIterable<Int> = arrayList<Int>(2, 3, 1)
+        expect(arrayList(1, 2, 3)) { list.sort() }
+        expect(arrayList(2, 3, 1)) { list }
+    }
+
+    test fun sortForIterable() {
+        val list : Iterable<Int> = listOf(2, 3, 1)
+        expect(arrayList(1, 2, 3)) { list.sort() }
+        expect(arrayList(2, 3, 1)) { list }
+    }
+
     class IterableWrapper<T>(collection : Iterable<T>) : Iterable<T> {
         private val collection = collection