- drop optional 2nd version arg from ghcdocdir, ghcpkgdir, and
        ghc_gen_filelists: multiversion subpackages are not supported
    - add ghcpkgbasedir
    - bring back some shared conditions which were dropped temporarily
    - test for ghcpkgdir and ghcdocdir in ghc_gen_filelists
    - allow optional pkgname arg for cabal_pkg_conf
    - can now package gtk2hs