Merge pull request #4950 from abeln/unreachable2

Add additional test case for #4661

Author: liufengyun

tests/patmat/t4661b.check

@@ -0,0 +1,2 @@
+10: Pattern Match Exhaustivity: _: c.Foo
+13: Match case Unreachable

tests/patmat/t4661b.scala

@@ -0,0 +1,15 @@
+class C {
+  trait Foo
+  class One extends Foo
+  class Two extends Foo
+  class Bla extends One
+}
+
+class Test(val c: C) {
+  import c._
+  def test(f: Foo) = f match { // not exhaustive
+    case f: One =>
+    case f: Two =>
+    case f: Bla => // unreachable case
+  }
+}