Random seed handling is too perilous

[nealey]

This just bit me in the rear: if you use the same seed for every puzzle, and the first thing you do is pick an answer, you get the same answer words every time.

We should have mothd set $SEED_BASE to the original value of $SEED, and then for every call out mkpuzzle or mkcategory, set SEED=${SEED_BASE}/${cat}/${points}.

If people really want the raw seed, they can get it, but by default they should just use $SEED, which will be unique for every puzzle.