data ExportEnv = ExportEnv Avails Fixities
type Avails = [AvailInfo]
-type Fixities = [(OccName, Fixity, Provenance)]
+type Fixities = [(OccName, (Fixity, Provenance))]
-- Can contain duplicates, if one module defines the same fixity,
-- or the same type/class/id, more than once. Hence a boring old list.
-- This allows us to report duplicates in just one place, namely plusRnEnv.