SI-6897, lubs and varargs star.

Don't allow lubs to calculate refinement types which contain
a varargs star outside of legal varargs star position.

Author: paulp

test/files/pos/t6897.scala

@@ -0,0 +1,6 @@
+class A {
+  val html = (null: Any) match {
+    case 1 => <xml:group></xml:group>
+    case 2 => <p></p>
+  }
+}