Added 'override' checks

idea/testData/codegen/bridge.jet

@@ -1,11 +1,11 @@
 import java.lang.Integer
 
 open class C {
- fun f(): Any = "C f"
+    virtual fun f(): Any = "C f"
 }
 
 class D() : C {
-    fun f(): String = "D f"
+    override fun f(): String = "D f"
 }
 
 fun box(): String{

idea/testData/codegen/classes/classObjectInterface.jet

@@ -2,7 +2,7 @@ class C() {
   fun getInstance(): Runnable = C
 
   class object: Runnable {
-    fun run(): Unit { }
+    override fun run(): Unit { }
   }
 }
 

idea/testData/codegen/controlStructures/forUserType.jet

@@ -70,24 +70,24 @@ fun box() : String {
 }
 
 class MyCollection1(): java.lang.Iterable<Int> {
-    fun iterator(): java.util.Iterator<Int> = MyIterator()
+    override fun iterator(): java.util.Iterator<Int> = MyIterator()
 
     class MyIterator(): java.util.Iterator<Int> {
         var k : Int = 5
 
-        fun next() : Int = k--
-        fun hasNext() = k > 0
+        override fun next() : Int = k--
+        override fun hasNext() = k > 0
     }
 }
 
 class MyCollection2(): Iterable<Int> {
-    fun iterator(): Iterator<Int> = MyIterator()
+    override fun iterator(): Iterator<Int> = MyIterator()
 
     class MyIterator(): Iterator<Int> {
         var k : Int = 5
 
-        fun next() : Int = k--
-        fun hasNext() = k > 0
+        override fun next() : Int = k--
+        override fun hasNext() = k > 0
     }
 }