Warning when no Haddock documentation installed could be rephrased, for accuracy

[mpilgrem]

Distribution.Simple.Haddock.haddockPackagePaths currently has (extract):

      warning =
        "The documentation for the following packages are not "
          ++ "installed. No links will be generated to these packages: "
          ++ intercalate ", " (map prettyShow missing)

The use of the The in The documentation implies that documentation exists but is not installed. In fact, the message is also generated when a package has no Haddock documentation for legitimate reasons (for example see the mtl-compat package, which can expose no modules for legitimate reasons).

I suggest this message should be re-phrased, as follows:

      warning =
        "The following packages have no Haddock documentation "
          ++ "installed. No links will be generated to these packages: "
          ++ intercalate ", " (map prettyShow missing)

I will raise a pull request, accordingly.