Both for geometric algebra and in general (since it's just in
unary_expr). However, it doesn't quite work for float stuff (eg,
`vector × vector`, but that's only because the anti-commutative flag
isn't set.
Result type and constant handling is now table-driven, resulting in the
removal of seven switch statements (and thus a lot less hassle when
extending types or expressions). Also, (u)long and (u)short are fully
implemented.
In addition, other than result type handing for boolean results, any
back-end specific implementation is now in the back-end.
