Minor forum upgrade completed

[Jazzy]

The forum has just been upgraded from phpBB3 rc5 to rc7, which is intended as one of the last unstable releases - a stable release is supposed to be happening fairly soon, but there were some big problems with rc6, from what I can gather. So, as before: no mods will be installed until we're on a stable release, which is to say not yet, and if there are any bugs, please post them here.