1.0.21.17: --script commandline argument

1.0.21.17: --script commandline argument

 * Works as both runtime and toplevel argument (which may imply the
   separation between the two is suspect?):

 * As a runtime argument it implies --noinform and the end of runtime
   arguments.

 * As a toplevel argument it implies --disable-debugger and the end of
   toplevel arguments. It additionally inhibits sysinit and userinit
   processing unless an explicit --userinit or --sysinit option is
   given before it.

   Then SBCL loads the specified specified file with :VERBOSE NIL and
   :PRINT NIL, discarding the first line if it start with #!.

   When the script file has been processed, SBCL exits without
   entering the REPL.

 * Documentation & a test.

 * Based loosely on an earlier patch by Kevin Reid.