Add test case

 - also rework previous test of #3189 to be a run test, just to make
   sure the problem is solved.

Author: odersky

tests/pos/i3168.scala

@@ -0,0 +1,14 @@
+object Test {
+  class C {
+    def foo(x: Int) = 1
+    def foo(x: Double) = 2
+  }
+
+  implicit class COps(val x: C) {
+    def foo(x: String) = 3
+  }
+
+  def test: Unit = {
+    (new C).foo("Hello")
+  }
+}

tests/pos/i3189.scala

@@ -0,0 +1,9 @@
+class Test[A](action: A => A) {
+  def this() = this(a => a)
+  def go(x: A) = action(x)
+}
+
+object Test extends App {
+  assert(new Test[Int]().go(3) == 3)
+}
+