running og forum with mysql 4

I've just patched og forum to run with mysql 4 as a quick favour for a friend. The code isn't neat and isn't optimised but we think it does the equivalent of the mysql 5 subselect stuff.

I'm posting it here so people can take it, check it (it seems to work hasn't been rigorously tested yet) and then hopefully integrate it nicely into either the main stream or into their own apps.