5.1 SERVER

Problem was caused by the COM_CHANGE_USER parsing code. That code ignored
character set number passed in COM_CHANGE_USER packet. Instead
character_set_client values was used. User name was not converted at all.

Fixed by using passed character set number to convert both db and user names.
If COM_CHANGE_USER does not contain character set number then
character_set_client is used to convert both names.