new_contents: _SCHEME = {
      'unix': {
          'prefix': '/usr/local',
          'eprefix': '$prefix',
          'bindir': '$eprefix/bin',
          'sbindir': '$eprefix/sbin',
          'libdir': '$eprefix/lib',
          'includedir': '$prefix/include',
          'datarootdir': '$prefix/share',
          'datadir': '$datarootdir',
          'mandir': '$datarootdir/man',
      }
  }
  
  _SCHEME_OPTS = {
      'prefix': {'opts': ['--prefix'],
                 'help': 'install architecture-independent files '
                         'in PREFIX [%s]'},
      'eprefix': {'opts': ['--exec-prefix'],
                 'help': 'install architecture-dependent files '
                         'in EPREFIX [%s]'},
      'bindir': {'opts': ['--bindir'],
                 'help': 'user executables [%s]'},
      'sbindir': {'opts': ['--sbindir'],
                 'help': 'system admin executables [%s]'},
      'libdir': {'opts': ['--libdir'],
                 'help': 'object code library [%s]'},
      'includedir': {'opts': ['--includedir'],
                 'help': 'C header files [%s]'},
      'datarootdir': {'opts': ['--datarootdir'],
                 'help': 'read-only arch.-independent data root [%s]'},
      'datadir': {'opts': ['--datadir'],
                 'help': 'read-only arch.-independent data [%s]'},
      'mandir': {'opts': ['--mandir'],
                 'help': 'man documentation [%s]'}
  }
  
  
  def get_scheme(platform, pkg_name):
      if platform.startswith('linux'):
          pkg_platform = 'unix'
      else:
          pkg_platform = platform
  
      try:
          scheme = _SCHEME[pkg_platform]
      except KeyError:
          raise ValueError("Platform %s not yet supported" % platform)
  
      scheme_opts = {}
      for k, v in _SCHEME_OPTS.items():
          val = _SCHEME_OPTS[k].copy()
          val['help'] = val['help'] % scheme[k]
          scheme_opts[k] = val
  
      return scheme, scheme_opts
  
subject: add a scheme factory for platform-specific path conventions.