fix, use dt_io_clear_zones() in all tools, fixes issue #80

Author: hroptatyr

src/dtest.c

@@ -142,9 +142,7 @@ main(int argc, char *argv[])
 		res = res == 1 || res == 0 ? 0 : 1;
 	}
 out:
-	if (fromz != NULL) {
-		zif_close(fromz);
-	}
+	dt_io_clear_zones();
 	if (argi->from_locale_arg) {
 		setilocale(NULL);
 	}

src/dzone.c

@@ -362,9 +362,6 @@ nor a date/time corresponding to the given input formats", inp);
 		free(d);
 	}
 
-	if (fromz != NULL) {
-		zif_close(fromz);
-	}
 	if (argi->from_locale_arg) {
 		setilocale(NULL);
 	}