• removed "portable" mode from shasum and addfile
  -- rarely used, mostly in outdated systems
  -- potentially confusing features (e.g. \r\r\n -> \n)
  -- Universal Newlines mode (-U) a much cleaner approach
  -- mimics Universal Newlines in Python
  
• shasum now uses Digest::SHA explicitly
  -- no longer loads Digest::SHA::PurePerl as an option
  -- hence no need for -R switch
  -- Digest::SHA::PurePerl has its own shasum: shasumpp