'cabal haddock --hyperlink-source' should use haddock '--hyperlinked-source' when available

[23Skidoo]

Saw this on Reddit today: https://www.reddit.com/r/haskell/comments/6o4rnb/psa_regarding_cabal_haddock/

PSA regarding cabal haddock
cabal haddock --haddock-option="--hyperlinked-source" is different from cabal haddock --hyperlink-source.
The former is how you create the nice haddocks that have links on every identifier in the highlighted source. The latter is how you get the old haddocks that just have hscoloured source pages.

I think we should update cabal haddock --hyperlink-source to make it use haddock --hyperlinked-source instead of hscolour when the version of Haddock is sufficiently new.