Tiny detail: the new DBTOEPUB macro definition in "src/Makefile.global.in" lacks another tab to be nicely aligned with the other definitions.
> and rebased this patch on top of that.
Applied and tested, everything looks fine.
The only remaining question is whether the xmllint check should always be called. You stated that it was stricter than sgml processing, so I would think it worth to always call it, but this is really a marginal preference. I think it is okay if some slaves in the build farm do build the various targets.