Prelude.Nat: add IsSucc predicate type
Prelude.Nat: add IsSucc predicate type

By popular demand.

kojiromike/Idris-dev,kojiromike/Idris-dev,kojiromike/Idris-dev,kojiromike/Idris-dev,kojiromike/Idris-dev,kojiromike/Idris-dev