Remove jkh from the list of current core team members (we're down to
seven now, but no election needed just yet).

Add jkh to the list of active developers (let's be optimistic: sysinstall2
is definitely coming now that jkh won't have to read core@ e-mail).

Add jkh to the list of core team alumni -- tentatively specify dates as
(1992-2002) but someone can tweak the first of those years as they see
fit (1992 is generally the lower bound across other entries).