Allow admin to disable explore mode

Some public servers want to disable explore mode, so
make it configurable in sysconf.

src/cmd.c

@@ -509,6 +509,14 @@ enter_explore_mode(VOID_ARGS)
     } else if (discover) {
 	You("are already in explore mode.");
     } else {
+#ifdef SYSCF
+	if (!sysopt.explorers ||
+	    !sysopt.explorers[0] ||
+	    !check_user_string(sysopt.explorers)) {
+	    You("cannot access explore mode.");
+	    return 0;
+	}
+#endif
 	pline(
 	 "Beware!  From explore mode there will be no return to normal game.");
 	if (paranoid_query(ParanoidQuit,

src/files.c

@@ -2184,6 +2184,9 @@ int		src;
 	} else if (src == SET_IN_SYS && match_varname(buf, "SHELLERS", 8)) {
 	    if (sysopt.shellers) free(sysopt.shellers);
 	    sysopt.shellers = dupstr(bufp);
+	} else if (src == SET_IN_SYS && match_varname(buf, "EXPLORERS", 7)) {
+	    if (sysopt.explorers) free(sysopt.explorers);
+	    sysopt.explorers = dupstr(bufp);
 	} else if (src == SET_IN_SYS && match_varname(buf, "DEBUGFILES", 5)) {
 	    if (sysopt.debugfiles) free(sysopt.debugfiles);
 	    /* if showdebug() has already been called (perhaps we've added

src/sys.c

@@ -33,6 +33,7 @@ sys_early_init()
 #endif
 	sysopt.env_dbgfl = 0;	/* haven't checked getenv("DEBUGFILES") yet */
 	sysopt.shellers = NULL;
+	sysopt.explorers = NULL;
 	sysopt.maxplayers = 0;	/* XXX eventually replace MAX_NR_OF_PLAYERS */
 
 		/* record file */