[mdb-dev] More changes in doc/Makefile.am

[Nirgal <con...@ni...>]

Attached is a patch I'd like to commit:
- Fix the html/install removal for "make clean"
- Fix test of "userguide" when making links
- Make must fail when openjade fails. Testing doc/book1.htm is not enough, for example when you have partial docbook installation.