Generate copy function for data classes

#KT-2779 Fixed

compiler/testData/codegen/dataClasses/copy/varInConstructorParams.kt

@@ -0,0 +1,29 @@
+data class A(var a: Int, var b: String) {}
+
+fun box() : String {
+    var result = ""
+    val a = A(1, "a")
+    val b = a.copy()
+    if (b.a == 1 && b.b == "a") {
+        result += "1"
+    }
+
+    val c = a.copy(a = 2)
+    if (c.a == 2 && c.b == "a") {
+        result += "2"
+    }
+
+    val d = a.copy(b = "b")
+    if (d.a == 1 && d.b == "b") {
+        result += "3"
+    }
+
+    val e = a.copy(a = 2, b = "b")
+    if (e.a == 2 && e.b == "b") {
+        result += "4"
+    }
+    if (result == "1234") {
+        return "OK"
+    }
+    return "fail"
+}