Use the correct setoid equality in algebra/gset and algebra/coPset.

This fixes issue #46.

algebra/coPset.v

@@ -8,7 +8,7 @@ generalize the construction without breaking canonical structures. *)
 Section coPset.
   Implicit Types X Y : coPset.
 
-  Canonical Structure coPsetC := leibnizC coPset.
+  Canonical Structure coPsetC := discreteC coPset.
 
   Instance coPset_valid : Valid coPset := λ _, True.
   Instance coPset_op : Op coPset := union.

algebra/gset.v

@@ -7,7 +7,7 @@ Section gset.
   Context `{Countable K}.
   Implicit Types X Y : gset K.
 
-  Canonical Structure gsetC := leibnizC (gset K).
+  Canonical Structure gsetC := discreteC (gset K).
 
   Instance gset_valid : Valid (gset K) := λ _, True.
   Instance gset_op : Op (gset K) := union.