do not generate delegates when the class already has such method either declared or delegated (report an ambiguity in this case)

Merge conflict resolved by committer

compiler/testData/codegen/classes/delegation3.kt

@@ -0,0 +1,35 @@
+trait One {
+  public open fun foo() : Int
+  public open fun faz() : Int = 10
+}
+trait Two {
+  public open fun foo() : Int
+  public open fun quux() : Int = 100
+}
+
+class OneImpl : One {
+  public override fun foo() = 1
+}
+class TwoImpl : Two {
+  public override fun foo() = 2
+}
+
+class Test2(a : One, b : Two) : Two by b, One by a {
+  public override fun foo() = 0
+}
+
+fun box() : String {
+    var t2 = Test2(OneImpl(), TwoImpl())
+    if (t2.foo() != 0)
+        return "Fail #1"
+    if (t2.faz() != 10)
+        return "Fail #2"
+    if (t2.quux() != 100)
+        return "Fail #3"
+    if (t2 !is One)
+        return "Fail #4"
+    if (t2 !is Two)
+        return "Fail #5"
+
+    return "OK"
+}