patch applied (ghc): When BUILD_DOCBOOK_HTML is NO, keep the rules, just omit the target

[Simon Peyton Jones]

Fri Mar  5 09:30:04 PST 2010  simonpj at microsoft.com
  * When BUILD_DOCBOOK_HTML is NO, keep the rules, just omit the target
  
    (and similarly for PS and PDF)
  
  The previous setup nuked the rules for making the documentation when
  BUILD_DOCBOOK_HTML=NO.  This meant that "make html" didn't work.
  
  There isn't any reason to nuke the rules (so far as Simon and I know).

    M ./rules/docbook.mk -20 +6

View patch online:
http://darcs.haskell.org/ghc/_darcs/patches/20100305173004-1287e-3df6a813fb0f6fc84683c13813da9014d4aaf6a0.gz