With the --yaffle flag, you get the old behaviour which is to invoke the
checker for the core theory (and all the tests are updated appropriately
for this).
Since the NF might refer to hole names, and those hole names might be
possible to evaluate now, we'll need to recalculate the expected type's
normal form before rerunning the delayed elaborator
Works by running all possible elaborators and checking that exactly one
succeeds. Still to do: pruning the list of elaborators by target type,
dealing with 'UniqueDefault', checking that delaying on failure works as
it should.
