[exim-dev] Doc building: SDOP version

I've just fixed a bunch of box overflows in SDoP document processing for
spec.xfpt -> spec.pdf.

I'm about to fix "table_warn_soft_overflow" being unrecognised by SDoP,
by removing it and possibly putting in a replacement, if I find one.

This option was probably supported by some old version. I'm using
sdop-0.70 from 28 Jan 2011. If you're using an older version, please
update for building the docs.

-Phil