[PATCH] Generate svn help and man pages from common source

Here's an old patch I wrote to generate svn help and man pages, and possibly book reference section, from a common source (XML).

The idea's just come up again in IRC discussion.

This patch was based on svn trunk @1456600, five years ago.

It was actually working at that time. It was a proof of concept and needs further work to improve how it's done.

-- 
- Julian