Added library for new equational constraint (:=:)

EQConstraints.curry

+module EQConstraints where
+
+infix 4 :=:
+
+(:=:) :: a -> a -> Success
+(:=:) external
+
+-- (:/=:) :: a -> a -> Success
+-- (:/=:) external

External_EQConstraints.hs

+import Debug.Trace as DT
+
+external_d_OP_colon_eq_colon :: Unifiable a => a -> a -> Cover -> ConstStore -> C_Success
+external_d_OP_colon_eq_colon = (=:=#)