Lift haxl bounds
haxl places a constraint on aeson which precludes the use of th-abstraction-0.5, which then results in the solver instead choosing aeson-0.9, which results in a broken install plan.
Also, apply some conservative ad-hoc constraints to the plan to ensure that this is easier to debug in the future.
Fixes ghc#23048 (closed).
Edited by Ryan Scott