backport rest of subpackaging improvements from f18 rawhide
    
    - let ghc_bin_install take an arg to disable implicit stripping for subpackages
    - fix doc handling of subpackages for ghc_without_shared
    - without ghc_exclude_docdir include doc dir also for subpackages
    - rename ghc_binlib_package to ghc_lib_subpackage
    - add ghc_lib_build_without_haddock
    - no longer drop into package dirs when subpackaging with ghc_lib_build and
      ghc_lib_install