Fix to bug #438 http://bugs.skysql.com/show_bug.cgi?id=438

Fixed some compiler warnings, added header includes, return values etc.

server/core/dbusers.c

@@ -42,6 +42,7 @@
 #include <skygw_utils.h>
 #include <log_manager.h>
 #include <secrets.h>
+#include <mysql_client_server_protocol.h>
 
 #define USERS_QUERY_NO_ROOT " AND user NOT IN ('root')"
 #define LOAD_MYSQL_USERS_QUERY "SELECT user, host, password, concat(user,host,password) AS userdata FROM mysql.user WHERE user IS NOT NULL AND user <> ''"