Bug#1126033: dh-haskell: dh_haskell_install_ghc_registration picks wrong public library

[Clint Adams]

Package: dh-haskell
Version: 0.6.13

dh_haskell_install_ghc_registration presumes that globwise the first
ghc-pkg config in a directory is for the public library.  This is
definitely not the case with f.ex. happy-lib.