1. Don't add changelog and other implementation specific nvi files because
this have changed from 1.79 and are probably not relevant in 1.81
2. Put back virecover.
3. Descend regularly to subdirs instead of Makefile hacks
4. Use USD.doc stuff from the 1.81 docs except for vi.ref which has
unfortunately been converted to texinfo. For that, we preserve
the original documents because we want to still be able to make
section 13 (building texinfo is not acceptable because it will not
have the same look and feel as the rest of the book)
5. Since the texinfo reference is probably better maintained, build
that too as a texinfo document.
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