Migrated to PHP5

I meant to do this a long time ago (and in fact, I thought I already had), but it's only been done now.
I've finally ditched PHP4, which is being officially ended at the end of this year.
I was having difficulty getting any PHP-related pages showing earlier... ...because due to a modification I made, both versions were trying to run
Oh well. Let me know if you see any odd problems with the site.