Re: enable jade warnings

Neil Conway wrote:
> Attached is a crude patch to enable some additional jade/openjade
> warnings. This should help us catch improper or ill-advised SGML in
> the docs.

If that doesn't create any new warnings on the current (fixed) code,
then I agree with this.  However, I'd like to see it factored more to
avoid repeating it for jade and nsgmls.  The warning flags are in fact
SP flags, not Jade flags; only Jade is built on top of SP.  So maybe
assign this to SPFLAGS and add that to both invocations.  (This is a
bit analogous to CPPFLAGS vs. CFLAGS.)