Bastian Kleineidam: the "build_scripts" command and changes

Bastian Kleineidam: the "build_scripts" command and changes
necessary to support it.

Details:
  - build command additionally calls build_scripts
  - build_scripts builds your scripts in 'build/scripts' and adjusts the
    first line if it begins with "#!" and ends with "python", optionally
    ending with commandline options (like -O, -t ...).  Adjusting means we
    write the current path to the Python interpreter in the first line.
  - install_scripts copies the scripts to the install_scripts dir
  - install_data copies your data_files in install_data. You can
    supply individual directories for your data_files:

    data_files = ['doc/info.txt', # copy this file in install_scripts dir
      ('testdata', ['a.dat', 'b.dat']), # copy these files in
                                        # install_scripts/testdata
      ('/etc', ['packagerc']),    # copy this in /etc. When --root is
                                  # given, copy this in rootdir/etc
    ]

    So you can use the --root option with absolute data paths.