Bug#1016650: haskell-devscripts: Support internal libraries

[Scott Talbert]

Package: haskell-devscripts
Severity: important

haskell-devscripts does not currently support packages with internal
libraries (correctly).  Partial support was added to support GHC
registration with a directory of files instead of a single file, where
the first file in the directory was selected, but this unfortunately was
too naive and does not work in all cases.

Packages currently have to be patched to remove the internal libraries
(e.g., attoparsec), so ideally we should add proper support for internal
libraries to the tooling.