chat date format not being expressed

I found a bug in the theming of custom date formats. The format was being saved in the variables table but wasn't being applied.

I found that the chatroom.them.inc was calling variable 'chatroom_msg_date_format' on line 169 in the theme_chatroom_message function.

The custom date format was being saved as chatroom__chat_date_format.

Changing 'msg' to 'date' in the variable name on line 169 fixed the problem.