Reported in Trac #7272.  "tv1" should be "tv2"!

However, things weren't as simple as they sound, because
treating (x:Open) as different from (x:*) gave rise to
new failures; see Note [Comparison with OpenTypeKind] in Type.

My hacky solution is to treat OpenKind as equal to * and #,
at least in Core etc.  Hence the faff in Type.cmpTc.

I do not like this.  But it seems like another messy consequence
of including sub-kinding.  Sigh.