darcs path: make build reports more accurate for the haddock step

[Andrea Vezzosi]

currently we get DocsOk even when no documentation is created because
the package doesn't contain any buildable library,
with the following two patches "cabal install" will check and avoid
running "setup haddock" if no documentation is going to be created
returning DocsNotTried.
A possible downside is that we don't get the warning that suggests
--executables anymore from "cabal install" (it's still printed when
running "cabal haddock"),
if that has to be restored we can make hasDocsToBuild print the
warning, or make it return the String instead of Bool.
We could also make the report even more accurate by making
hadDocsToBuild return a list of the components of the package for
which it'll produce documentation.
The whole thing is a bit nasty without a specified semantic for the
Setup haddock command to be respected by Custom build systems.

Mon Jul  6 11:23:55 CEST 2009  Andrea Vezzosi <sanzhiyan at gmail.com>
  * expose hasDocsToBuild from D.S.Haddock

Mon Jul  6 16:41:00 CEST 2009  Andrea Vezzosi <sanzhiyan at gmail.com>
  * make build reports more accurate for the haddock step
-------------- next part --------------
A non-text attachment was scrubbed...
Name: expose-hasdocstobuild-from-d_s_haddock.dpatch
Type: application/octet-stream
Size: 39158 bytes
Desc: not available
Url : http://www.haskell.org/pipermail/cabal-devel/attachments/20090706/9c4a7162/expose-hasdocstobuild-from-d_s_haddock-0001.obj
-------------- next part --------------
A non-text attachment was scrubbed...
Name: make-build-reports-more-accurate-for-the-haddock-step.dpatch
Type: application/octet-stream
Size: 28616 bytes
Desc: not available
Url : http://www.haskell.org/pipermail/cabal-devel/attachments/20090706/9c4a7162/make-build-reports-more-accurate-for-the-haddock-step-0001.obj