1.0.48.33: --script bits and pieces

1.0.48.33: --script bits and pieces

 * Leaving out the script name means to read the script from standard
   input. In this case the shebang line is _not_ handle -- simply
   because I ran out steam. (Our shebang line processing assumes a
   seekable stream.)

 * Stream errors on standard streams cause scripts to exit silently.
   lp#770222.

 * Scripts no longer us *TTY* for *TERMINAL-IO*, but make up a two-way
   stream from *STDIN* and *STDOUT*. Similarly for *DEBUG-IO* but
   using *STDERR*. This means that backtraces from errors are now
   neatly captured in the standard error stream.