Restrict haddock to <= 2.9.2
Restrict haddock to <= 2.9.2

Ratio:

* haddock > 2.9.2 is meant for ghc-7.2, but ghc-7.2 is not widely used,
  yet.

* haddock > 2.9.2 does not even build with ghc-7.2 due to an issue with
  xhtml.

sol/doctest,snoyberg/doctest-haskell,ekmett/doctest,snoyberg/doctest-haskell,ekmett/doctest,sol/doctest