Add neg test

Author: odersky

tests/neg/i11899.scala

@@ -0,0 +1,12 @@
+
+
+import java.util.function.Function
+
+class Future[T](val initial: T) {
+  def map[V](v: V): Unit = println(v)
+  def map[U](fn: Function[T, U]): Unit = println(fn(initial))
+}
+
+val f = new Future(42)
+val fn = (i: Int) => i.toString
+val x = f.map(fn)  // error