Add scala#4884 test case

Author: odersky

tests/pos/i4884.scala

@@ -0,0 +1,13 @@
+object Test {
+  trait A
+  trait TestConstructor1 { type F[_ <: A] }
+  trait TestConstructor2[D] { type F[_ <: D] }
+
+  val v1: TestConstructor1 => Unit = { f =>
+    type P[a <: A] = f.F[a] // OK
+  }
+
+  val v2: TestConstructor2[A] => Unit = { f =>
+    type P[a <: A] = f.F[a] // Error! Type argument a does not conform to upper bound D
+  }
+}