various minor backports
    
    - add new names ghc_html_dir, ghc_html_libraries_dir, and ghc_html_pkg_dir
    - correct cabal-tweak-flag error message for missing flag (#1184508)
    - ghc-deps.sh: support ghc-pkg for ghc builds <= 7.4.2 as well
    - improve ghc_fix_dynamic_rpath not to assume cwd = pkg_name
    - fix warning in macros.ghc-extra about unused pkgnamever