Haddock version during build

[Simon Marlow]

So Simon PJ and I just discussed this, and we have a rough plan.

The basic problem is that in order to build documentation for the libraries 
in a GHC build tree using Haddock 2, we have to build Haddock 2 using the 
stage2 GHC.  There's no alternative, because when running Haddock against 
one of the packages in the build tree, it needs to read the interface files 
for the other packages.

So the rough plan is this: if we need to build documentation during a 
build, then we check out a copy of Haddock into the build tree (it's still 
a separate repository, like the libraries), and we build Haddock after 
stage 2, before generating the documentation.  We don't have to ship this 
Haddock with GHC, it's just a temporary build tool.

Sound reasonable?

Cheers,
	Simon