Minimise data stored in AvailInfo; lookup selectors in gresFromAvail
Move FieldLabel from TyCon to DataCon
GHC.getPackageModuleInfo now returns Nothing in minf_rdr_env
Significant reorganisation to solve constraints on the fly, rather than doing funny instance scoping
Restore selector names to Avail (again), because we need to know their module
Refactor field instance lookup
Revert "Add warning when a qualified name is used for an overloaded record field"

Make it an error instead.

This reverts commit 3bcee55ad72b0b07079d4f174b2b9fc7994dd1d2.
Correct error message for unsolved constraint due to field not in scope
Subtle points about SetResult instances given PolyKinds or TypeFamilies