Overriden setter now cannot weaken visibility #KT-3369 Fixed

compiler/testData/diagnostics/tests/OverridenSetterVisibility.kt

@@ -0,0 +1,29 @@
+public interface ITest {
+    public var prop : Int
+        get() = 12
+        set(value) {}
+}
+
+abstract class ATest {
+    protected open var prop2 : Int
+        get() = 13
+        set(value) {}
+}
+
+class Test: ATest(), ITest {
+    override var prop : Int
+        get() = 12
+        <!CANNOT_WEAKEN_ACCESS_PRIVILEGE!>private<!> set(value) {}
+
+    override var prop2 : Int
+        get() = 14
+        <!CANNOT_CHANGE_ACCESS_PRIVILEGE!>internal<!> set(value) {}
+}
+
+fun main(args: Array<String>) {
+    val test = Test()
+    <!INVISIBLE_SETTER!>test.prop<!> = 12
+
+    val itest: ITest = test
+    itest.prop = 12 // No error here
+}

compiler/testData/diagnostics/tests/OverridenSetterVisibility.txt

@@ -0,0 +1,27 @@
+package
+
+public fun main(/*0*/ args: kotlin.Array<kotlin.String>): kotlin.Unit
+
+public abstract class ATest {
+    public constructor ATest()
+    protected open var prop2: kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public interface ITest {
+    public open var prop: kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public final class Test : ATest, ITest {
+    public constructor Test()
+    public open override /*1*/ var prop: kotlin.Int
+    protected open override /*1*/ var prop2: kotlin.Int
+    public open override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String
+}