Add tests

Adds the original test form #1381. t2660 looks similar.
Also adds some unrelated tests I had in the queue that now
compile.

Author: odersky

tests/pos/hkgadt.scala

@@ -0,0 +1,9 @@
+object HKGADT {
+  sealed trait Foo[F[_]]
+  final case class Bar() extends Foo[List]
+
+  def frob[F[_]](foo: Foo[F]) =
+    foo match {
+      case Bar() => ()
+    }
+}

tests/pos/i618.scala

@@ -0,0 +1,3 @@
+class C(val f: Any*)
+
+class D(override val f: Nothing) extends C(f)

tests/pos/overloaded.scala

@@ -57,3 +57,30 @@ object overloaded {
   val a: A = fr(new C)
   val b: B = fr(new C)
 }
+
+// from #1381
+
+object Foo {
+  class Bar[T]
+  implicit def const[T](x: T): Bar[T] = ???
+
+  def bar[T](e: T): Any = ???
+  def bar[T](e: Bar[T]): Any = ???
+
+  val b: Bar[Int] = ???
+  bar(b)
+}
+
+object Test2 {
+    trait A; trait B
+    class C1 {
+       def f(x: A): Unit = println("A")
+    }
+    class C2 extends C1 {
+       def f(x: B): Unit = println("B")
+    }
+    object Test extends C2 with App {
+      implicit def a2b(x: A): B = new B {}
+      f(new A {})
+    }
+}