Fix calls to extensions where the result is already a dot list.
Fix evalTypeList where the argument of a TDotable is a TDotable.
Fix evalTypeList for more complex cases.
Correctly handle non-recursively rectangular datatype and channels.

I'm not really sure we should allow these, but FDR2 does, and I can see
why we need to support something like them.
Add prioritise_nocache.
Add support for another type of dot list in the typechecker.

This is an easy one to support, thankfully.