Redo division and remainder specs.
Redo division and remainder specs.

This makes there be two pairs of functions, `div` `mod` and `divEu`
`modEu`. The first pair are the CS traditional pair of truncated
division and its associated remainder (sign follows left-hand side).
The `Eu` functions are Euclidean division and its associated
remainder (sign is always positive).

danfuzz/samizdat,danfuzz/samizdat,danfuzz/samizdat,danfuzz/samizdat