1.0.48.29: better end-of-the-world handling

1.0.48.29: better end-of-the-world handling

 * Implicit QUIT.

 * Make sure we have %END-OF-THE-WORLD visible while doing cleanups.

 * Handle errors from cleanups.

 * Disable interrupts in places where the environment might now be up to
   handling them yet/anymore.

 * If user calls QUIT, and exit hooks run without serious trouble, report the
   exit status requested even if there is trouble later flushing streams, etc.

 * Also make SAVE-LISP-AND-DIE signal an error if SAVE returns. (When there is
   eg. a file with the desired name but insufficient permissions.)