The parallel codepath was incorrectly retypechecking the
hs-boot ModIface prior to typechecking the hs file,
which was inconsistent with the non-parallel case. The
non-parallel case gets it right: you don't want to retypecheck
the hs-boot file itself (forwarding its declarations to hs)
because you need it to be consistently knot-tied with itself
when you compare the interfaces.
Signed-off-by: Edward Z. Yang <email@example.com>