Fix: cabal-debian 4.33-4 cannot detect GHC built-in packages correctly

[Kei Hibino <ex8k.hibino@gmail.com>]

Hi,

I reported and fixed the problem of cabal-debian around detecting GHC built-ins.

cabal-debian searches `package.conf.d' from output of `dpkg -L ghc',
for example under `/var/lib/ghc/package.conf.d/',
and matches filenames like `base-4.9.0.0.conf'.
Under ghc-7.10, checksum suffix exists like
`base-4.8.2.0-0d6d1084fbc041e1cded9228e80e264d.conf',
but under ghc-8 it does not.

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=850920

https://lists.alioth.debian.org/pipermail/pkg-haskell-commits/2017-January/043666.html
https://lists.alioth.debian.org/pipermail/pkg-haskell-commits/2017-January/043667.html

Please review this fix, and upload.

Regards