Fix SigTvs at the kind level

Authored by simonpj on Dec 11 2017, 9:53 AM.

Description

Fix SigTvs at the kind level

This patch fixes two bugs in the treatment of SigTvs at the
kind level:

  • We should check if they get unified with each other (Trac Trac #11203)

Both are described in TcHsType

Note [Kind generalisation and SigTvs]