it's just been added by me. (it's not xemacs dependent but paredit dependent that i didn't notice due to my shared init.el file).

please apply the attached patch:

2006-11-03  Attila Lendvai  <attila.lendvai@gmail.com>
   
    * slime.el (slime-repl-kill-input): Also reset the history
    navigation and when point is right after the prompt then delete
    the entire repl input.
    (slime-repl-delete-from-input-history): New. Deletes the current
    repl input from the history when navigating the history. Bound to
    "\M-\C-d". Unfortunately slime-repl-merge-histories currently
    loads them back when the history is saved.
    (sldb-sexp-highlight-mode): Handle case when paredit is not
    loaded.

hth,