Bug#842549: Dh_Haskell.sh should respect DH_VERBOSE settings

[Matthias Klose]

Package: src:haskell-devscripts
Version: 0.12

I'm trying to debug an internal compiler error (not knowing anything about
haskell), and would like to see the commands being run during the build; however
even Dh_Haskell.sh doesn't respect the DH_VERBOSE settings, and it's not obvious
from the build script, how ghc is invoked, so that you can re-run the command in
question.