Renamed error code method

Author: mmottl

src/postgresql.ml

@@ -626,7 +626,7 @@ object
 
   method error_field field_name = Stub.result_error_field res field_name
 
-  method sqlstate_error_code =
+  method error_code =
     Error_code.of_sqlstate (Stub.result_error_field res Error_field.SQLSTATE)
 
   method ntuples = ntuples

src/postgresql.mli

@@ -226,8 +226,8 @@ class type result = object
   method error_field : Error_field.t -> string
   (** [#error_field] @return message of given error field in a result. *)
 
-  method sqlstate_error_code : Error_code.t
-  (** [#sqlstate_error_code] @return the error code of the error condition
+  method error_code : Error_code.t
+  (** [#error_code] @return the error code of the error condition
       as stored in the SQLSTATE field. *)
 
   (** Retrieving SELECT Result Information *)