src/docs/design and make distcheck

[John Ralls]

The Makefile in src/docs/design requires texi2dvi, which in turn depends on TeX. Make distcheck insists on actually building src/docs/design.

Does that even make sense? Setting aside the fact that those design documents are horribly out of date (the last substantive change was 7 years ago), it's arguable that we should just delete the whole thing (Christian added a warning about their being obsolete 4 years ago). But it seems really dumb to have an enormous dependency (MacTeX is a 1.8 GB download) to make a PDF of a wrong document.

Regards,
John Ralls