Made the test case for bug #15917 independent on platforms.

mysql-test/r/having.result

@@ -360,8 +360,6 @@ s1	count(s1)
 y	1
 drop table t1;
 DROP SCHEMA IF EXISTS HU;
-Warnings:
-Note	1008	Can't drop database 'HU'; database doesn't exist
 CREATE SCHEMA HU ;
 USE HU ;
 CREATE TABLE STAFF

mysql-test/t/having.test

@@ -354,7 +354,9 @@ drop table t1;
 # when the server is run on Windows or with --lower-case-table-names=1
 #
 
+--disable_warnings
 DROP SCHEMA IF EXISTS HU;
+--enable_warnings
 CREATE SCHEMA HU ;
 USE HU ;