Add test cases for scala#3965

What happened was that a higher-kinded type was added repeatedly
to a constraint. Because equality of higher-kinded types was broken,
the compiler did not realize that the type had already been added.

Author: odersky

tests/pos/i3965.scala

@@ -0,0 +1,19 @@
+trait Iterable[+A] extends  IterableOps[A, Iterable, Iterable[A]]
+trait IterableOps[+A, +CCop[_], +C]
+
+trait SortedSet[A] extends Iterable[A] with SortedSetOps[A, SortedSet, SortedSet[A]]
+
+trait SortedSetOps[A, +CCss[X] <: SortedSet[X], +C <: SortedSetOps[A, CCss, C]]
+
+class TreeSet[A]
+  extends SortedSet[A]
+    with SortedSetOps[A, TreeSet, TreeSet[A]]
+
+class Test {
+  def optionSequence1[CCos[X] <: IterableOps[X, CCos, _], A](xs: CCos[Option[A]]): Option[CCos[A]] = ???
+  def optionSequence1[CC[X] <: SortedSet[X] with SortedSetOps[X, CC, CC[X]], A : Ordering](xs: CC[Option[A]]): Option[CC[A]] = ???
+
+  def test(xs2: TreeSet[Option[String]]) = {
+    optionSequence1(xs2)
+  }
+}

tests/pos/i3965a.scala

@@ -0,0 +1,15 @@
+trait SortedSet[A] extends SortedSetOps[A, SortedSet, SortedSet[A]]
+
+trait SortedSetOps[A, +CC[X] <: SortedSet[X], +C <: SortedSetOps[A, CC, C]]
+
+class TreeSet[A]
+  extends SortedSet[A]
+    with SortedSetOps[A, TreeSet, TreeSet[A]]
+
+class Test {
+  def optionSequence1[CC[X] <: SortedSet[X] with SortedSetOps[X, CC, CC[X]], A : Ordering](xs: CC[A]): Unit = ()
+
+  def test(xs2: TreeSet[String]) = {
+    optionSequence1(xs2)
+  }
+}