- rewrite shebangs by default (disable via --no-shebang-rewrite),
    examples:
     + "/usr/bin/env python*" → "/usr/bin/python*"
     + "/usr/local/bin/python foo" → "/usr/bin/python foo"
     + "/usr/bin/python2" → "/usr/bin/python"
  - new --shebang option to replace all shebangs in bin dirs
    (example: --shebang /usr/bin/python2.6)