Fix for SI-4744, another variety of cycle.

I threw this in with the previous commit behind -Ybreak-cycles, but
this one is much less sketchy. Explanation: have to handle f-bounds
more deftly. Namers forces lower bounds to prevent recursion in
that direction, but a light touch is required to handle these two
situations differently:

  // This is a cyclic type parameter - an error is correct
  class A[T <: Comparable[_ <: T]]

  // This is not cyclic - it flips the arrow
  class B[T <: Comparable[_ >: T]]

Long have I been haunted by the knowledge that you can
write class B in java, but not in scala:

  public class B<T extends Comparable<? super T>> {}

It's over! We've achieved parity with java.

1 files changed, 1 insertions, 0 deletions

diff --git a/test/files/pos/t4744.flags b/test/files/pos/t4744.flags
new file mode 100644
index 0000000000..ca20f55172
--- /dev/null
+++ b/test/files/pos/t4744.flags
@@ -0,0 +1 @@
+-Ybreak-cycles