change #vanquished from wizard mode to normal play

Make the existing '#vanquished' command be available during regular
play, with M-V bound to it.  'm #vanquished' or 'm M-V' brings up
the sorting menu that you get when answering 'a' rather than 'y' at
the end-of-game "disclose vanquished creatures?" prompt.

The original #vanquished came from slash'em, where it was available
in normal play.  When added to nethack, it was put in as wizard-mode-
only. I added the sorting capability several years ago.

The chosen sort is remembered and re-used if not reset but only for
the remainder of the current session.  It probably ought of become
a run-time option so be settable in advance and across sessions but
I haven't done that.

src/cmd.c

@@ -2724,8 +2724,8 @@ struct ext_func_tab extcmdlist[] = {
     { '<',    "up", "go up a staircase",
               /* (see comment for dodown() above */
               doup, CMD_M_PREFIX, NULL },
-    { '\0',   "vanquished", "list vanquished monsters",
-              dovanquished, IFBURIED | AUTOCOMPLETE | WIZMODECMD, NULL },
+    { M('V'), "vanquished", "list vanquished monsters",
+              dovanquished, IFBURIED | AUTOCOMPLETE | CMD_M_PREFIX, NULL },
     { M('v'), "version",
               "list compile time options for this version of NetHack",
               doextversion, IFBURIED | AUTOCOMPLETE | GENERALCMD, NULL },