old_contents: version_info = (0, 4, 0)
  __version__ = '.'.join(map(str, version_info[:3])) + ''.join(version_info[3:])
  
new_contents: version_info = (0, 4, 0, 'dev')
  __version__ = '.'.join(map(str, version_info[:3])) + ''.join(version_info[3:])
  
subject: set master to dev version