ilog: relicense to Public Domain.

ilog: relicense to Public Domain.

I noted to Timothy in 2011:
   I finally got around to implementing license checking in ccanlint,
   and it shows that your public domain ccan/isaac module uses your LGPL
   ccan/ilog module, which partially defeats the point.

   You and I are the only ones who did anything significant to ilog; I'm
   happy to relicense to PD or whatever else you want.  Or leave it, in
   which case I'll need to document it clearly.

He finally got back to me, and I sent him this patch, to which he replied:

     Ack.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>