Correctly locate Haddocks in hoogle-local expression

On some versions of GHC, documentation is at, for example:

    LIB/share/doc/

In others, it is at:

    LIB/share/doc/x86_64-darwin-ghc7.6.3/

This change will pick up documentation first from the second location, then
from the first.
Merge pull request #2754 from jwiegley/lhfix

Fix to local Hoogle expression