64-bit dnscache, anyone?

I think I got this working last night, for certain definitions of
'working'.  I've got a dnscache that starts, allocates > 4GiB and
answers queries.  I started with Matthew Dempsky's patch:

http://shinobi.dempsky.org/~matthew/patches/djbdns-cache64.patch

...but had to tweak alloc.c a bit, too.

I'm going to see about making a compile time option to the configure
script to enable a 64-bit cache if you want it (and have the
hardware).

I'm working on a synthetic test at the moment to exercise the cache,
but it would be good to have a real world test.  Anybody want to take
this for a spin?